Esser, Frederick: John Locke‘s Investigation into our Knowledge of Bodies


Kapitel 10. Scope and Advancement of Knowledge

After having assessed contemporary knowledge of bodies, Locke sums up his results as to its extent by declaring that our knowledge is “very short and scanty“, namely that we have “very little general Knowledge“.<592> Locke‘s rather general programmatic statements in the introductive part of the Essay also relate to the knowledge of bodies where insight in the nature of contemporary knowledge is said to make plain which inquiries are intelligible and worth to be investigated and which are not.<593> This means, Locke takes his disenchanting results of his analysis to pave the way for an intelligible conception of a science of bodies.

I will examine in which sense for Locke contemporary knowledge of bodies is “very short and scanty“ and how this pertains to the advancement of knowledge. As will be delineated, Locke specifies knowledge in two ways, namely quantitatively and qualitatively. He thus effectively assesses and judges contemporary knowledge of bodies in the perspective of an ideally scientific account, indirectly developing a conception of an ideal science of bodies. I want to emphasize that not only virtually all bits of the account relate to an ideal theory of bodies, but more importantly, that his final judgement does so as well, namely that knowledge is “very short and scanty“. The upshot is that one does not know much of importance compared to what one ideally should know and that which one knows is in fact trivial. In the same perspective one has to read Locke‘s proposal of so-called remedies, i. e. general means, to enhance knowledge. The aim of Locke‘s assessment thus turns out to establish first that from an ideal epistemological perspective contemporary knowledge of bodies has limited value to develop then an appropiate conception of a contemporary science of bodies to enlarge human knowledge. Moreover, as will be contended, Locke‘s claim that the real essences of bodies are prima facie specific form the backdrop of why his chief issues are problematic for him. One has to take into account his views on real essences to understand comprehensively why for


him contemporary knowledge of bodies has scarcely any epistemic value and why this insight paves the way for an appropriate conception to enhance knowledge. But most importantly, an unorthodox reading of the nature of Locke‘s ideal science of bodies will be advanced. Locke does not hold on to a Cartesian or rationalistic idea that conceives an ideal science as an a priori account which, roughly speaking, deduces properties from the microphysical figure of bodies, but rather develops a genuine empiristic conception.

The first two sections discuss Locke‘s assessment of the scope of human knowledge of bodies. The first one reconstructs the extent of knowledge which quantitatively determines the extent of contemporary knowledge. The second one determines Locke‘s account with respect to his other issues where he qualitatively assesses human knowledge, namely to which degree it is “real“ and “instructive“. Not unimportantly with respect to Locke‘s own view on remedies, in this context he rejects the Aristotelian conception of maxims, i. e. propositions conceived as being essential for the advancement of knowledge. Subsequently, the nature of Locke‘s conception of an ideal science of bodies will be reconstructed on the background of the foregoing accounts. This will then be contrasted with Locke‘s proposal of remedies which amounts to a conception of a contemporary science of bodies. Finally, Locke‘s view on the prospects of such a science of bodies will be highlighted. This outlook is not advanced in a separate chapter or discussion, but is present in many contexts. A sharp contrast will emerge between what Locke takes as an ideal comprehension of bodies and the kind of knowledge he believes humans can ever attain - if God is not so kind as to reveal it to us one day.

a. The Extent of Human Knowledge of Bodies

Locke discusses the extent of knowledge in terms of his distinction of knowledge in four realms: identity and diversity, coexistence of properties, relations, and real existence.<594> With respect to bodies, the analysis focuses on coexistence and we will therefore discuss this realm first.

The coexistence of properties pertains exclusively to bodies since coexisting properties are


understood to be physical features of bodies which go constantly together with the features included in the idea of a species. For example, given that gold is defined as the kind of substances being yellow and soluble in aqua regia, the proposition ’Gold is fixed‘ expresses that the feature of fixedness coexists with the defining properties of gold. Everything what is gold, is fixed. Locke maintains that we have knowledge of coexisting properties, namely scanty intuitive knowledge. One can distinguish between two kinds of knowledge. First, there is knowledge of the coexistence of primary qualities. Locke mentions few instances, for instance: to have figure entails the possession of extension, to pass on or receive motion by impulse supposes solidity, and to be both solid and in space implies the filling of space.<595> Second, we have intuitive knowledge of the repugnancy of secondary qualities: secondary qualities being determined features of the same determinable properties do not coexist, since the possession of one of them excludes the possession of the others. Take, for example, colours. If gold is defined by being yellow, one (intuitively) knows that gold does not have another colour in addition.

Thus, for Locke there is hardly any intuitive knowledge of the repugnancy or coexistence of primary and secondary qualities. Locke is certainly right with this judgement, given the small number of propositions in comparison to what one should ideally know. On the other hand, the mentioned knowledge of coexisting primary qualities amounts to not less than knowledge of fundamental laws: to have figure entails the possession of extension, being capable of passing on or receiving motion by impulse supposes to be solid, and being both solid and in space implies the filling of space.<596>

Yet, even though we have only scanty intuitive knowledge of coexisting properties, maybe we have demonstrative knowledge? According to Locke, however, there is no demonstrative knowledge of coexistent qualities. This is in effect not surprising, since intuitively known propositions are the basis for demonstrations. But Locke further specifies the reasons for our ignorance.

Locke‘s paradigm for demonstrative knowledge of coexisting properties is knowledge of the coexistence of a secondary quality, i. e. the ascription of a feature to specimens of a sort


which is not defined by this secondary quality. This becomes plain when Locke illustrates our ignorance:

“Thus though we see the yellow Colour, ad upon trial find the Weight, Malleableness, Fusibility, and Fixedness, that are united in a piece of Gold; yet because no one of these Ideas has any evident dependence, or necessary connexion with the other, we cannot certainly know, that where any four of these are, the fifth will be there also [...].“<597>

Given Locke‘s general conception of demonstrative knowledge, our lack of it means that one does not perceive a necessary connection holding between the respective properties. The reason for our general ignorance of the coexistence of secondary qualities consists in our ignorance of a necessary connection holding between the set of properties defining the sort and the secondary quality in question. Thus, the question arises what kind of necessary connection is preeminent for demonstrative knowledge of the coexistence of secondary qualities.

Knowledge of such a necessary connection, Locke contends, comprises of two parts. First, one has to grasp the defining features of the sort in terms of microphysical primary qualities, i. e. one has to know the properties which on the explanatory stage correspond to the defining features of the macrophysical stage.<598> This is a necessary condition, Locke argues. For, since secondary qualities depend on microphysical primary qualities, one has to understand the defining properties in terms of microphysical primary qualities in order to conceive that a secondary quality depends on this set of defining features. Thus, if one does not know the defining features in terms of microphysical primary qualities, one cannot know whether a secondary quality depends on, or respectively is determined by, the defining set. This means in turn, knowledge of a necessary connection between a (secondary) quality and the defining features entails knowledge of the defining properties in terms of primary qualities.

Second, one has to comprehend the necessary connection between a secondary quality and the microphysical primary qualities on which it depends.<599> Locke conceives this


necessary connection to be the causal relationship holding between the microphysical primary qualities, which correspond to a secondary quality, and the idea of the secondary quality. This manifests in his claim that one has “to discover [a] connexion betwixt these [microphysical] primary qualities of Bodies, and the sensations that are produced in us by them [to] be able to establish certain and undoubted Rules of the Consequence or Co-existence of any secondary Qualities“.<600> This likewise becomes plain when Locke admits that in this context he presumes the corpuscularian hypothesis to highlight the matter.<601> This means, to know that a secondary quality depends on its corresponding microphysical primary qualities is to grasp that the latter causes an idea of the former. The backdrop of this claim is Locke‘s definition of qualities. Secondary qualities are understood as the properties causing a specific idea (of a reducible, non-real quality), i. e. a secondary quality is grasped in virtue of the idea that it causes. The idea apparently is: to know that a secondary quality truly depends on a certain set of microphysical primary qualities, one has to grasp that the idea of the secondary quality is genuinely caused by this set of features.

Locke‘s understanding of demonstrative knowledge of the coexistence of secondary qualities thus comprises two parts: the comprehension of the defining features of a sort and of the secondary quality in terms of microphysical primary qualities, and the grasp of the causal relationship holding between the secondary quality (conceived in microphyiscal terms). The point is of course that the second part shows which microphysical properties cause one‘s idea of a secondary quality, i. e. which microphysical features are to be identified as the secondary quality, whereas the first part imparts that these microphysical properties are features of the microphysical structure that is identical with the defining properties of the species. Evidently, knowledge of these two parts is sufficient for Locke to attain demonstrative knowledge of coexisting properties. To be precise, the so far advanced reconstruction applies only when species are defined in microphysical terms. If a sort is defined by secondary qualities, one has to grasp the causal relationships between these features and their ideas as well in order to know with which


microphysical primary qualities one has to identify the secondary qualities.

Moreover, strictly speaking, this depiction works only for sensible qualities, and has to be supplemented by an analogous condition for non-sensible secondary qualities. For instance, knowledge of the coexistence of the defining properties of wax with the secondary quality of being able to be melted by the sun presupposes knowledge of the causal relationship between the sun‘s capacity to melt wax and the wax‘s quality to be melted by the sun, since the wax‘s secondary quality to be melted by the sun is defined in relation to the sun‘s power to melt wax. That is, there is a third aspect, namely the grasp of the causal relationship in explanatory terms which holds between a secondary quality and the feature of another body in terms of which the secondary quality is understood. On first thought, however, Locke does not seem to acknowledge this consequence for knowledge of coexisting non-sensible secondary qualities:

“§16. But as to the Powers of Substances to change the sensible Qualities of other Bodies, which make a great part of our Enquiries about them, and is no inconsiderable branch of our Knowledge; I doubt, as to these, whether our Knowledge reaches much farther that our Experience; or whether we can come to the discovery of most of these Powers, and be certain that they are in any Subject by the connexion with any of those Ideas, which to us makes its Essence. Because the Active and Passive Powers of Bodies, and their ways of operating, consisting in a texture and motion of Parts, which we cannot by any means come to discover: ‘Tis but in very few Cases, we can be able to perceive their dependence on, or repugnance to any of those Ideas, which make our complex one of that sort of Things.“<602>

The point is that Locke does not explain the difficulty and bleak prospects of discovering coexisting non-sensible secondary qualities by the difficulty to acquire a causal understanding of sense perception, as he does in the case of sensible qualities.<603> He rather points to the hurdle of grasping microphysical properties and processes. And he likewise maintains the possibility of attaining knowledge of non-sensible dispositional properties if one knows the internal constitutions of bodies.<604> This implies, according to Locke, one can have knowledge of coexisting non-sensible qualities even though one does not grasp


microphysical processes. Below, I will come back to this claim when further clarifying the nature of necessary connections.<605> The important bit is that Locke can maintain these contentions only if he conceives here non-sensible dispositions from a microphysical perspective. If pressed, he has to concede that knowledge of coexisting non-sensible secondary qualities involves necessary connections partly relating to sense perceptions, if the properties are grasped by the change of sensible qualities in bodies.

In this perspective, one has also to read the last sentence of the quote where Locke asserts that we have knowledge of the coexistence or repugnance of non-sensible dispositions.<606> Given that Locke can hardly claim that reflection on our everyday ideas reveals the coexistence of this kind of properties, he must mean the repugnance of features. For instance, the defining power of gold to be soluble in aqua regia implies knowledge that gold is not non-soluble in aqua regia Epistemologically speaking, this kind of knowledge is of course not much worth and it is not very much compared to the countless unknown, coexisting secondary qualities whose high number Locke emphasizes.<607> To make sense of Locke, one has to understand in this way his contention that there are a few cases of knowing the coexistence or repugnance of non-sensible dispositions.

Implicitly, the discussion of non-sensible secondary qualities has already depicted Locke‘s model of necessary connections as to coexisting microphysical primary qualities. For him, demonstrative knowledge of the operations of bodies in microphysical terms involves a necessary connection solely holding between microphysical primary qualities. In this passage, Locke‘s position is again manifest that he conceives the attainment of this kind of knowledge as more probable than the comprehending of sense perception and of the coexistence of sensible qualities:

Ҥ13. That the size, figure, and motion of one Body should cause a change in the size, figure, and motion of another Body, is not beyond our Conception; the separation of the Parts of one Body, upon the intrusion of another; and the change


from rest to motion, upon impulse; these, and the like, seem to us have some connexion one with another. And if we knew these primary Qualities of Bodies, we might have reason to hope, we might be able to know a great deal more of these Operations of them upon another: But our Minds not being able to discover any connexion betwixt these primary qualities of Bodies, and the sensations that are produced in us by them, we can never be able to establish certain and undoubted Rules of the Consequence or Co-existence of any secondary Qualities, though we could discover the size, figure, or motion of those invisible Parts, which immediately produce them.“<608>

It becomes plain that in the case of bodies necessary connections are conceived as causal relationships. Given Locke‘s view of what demonstrative knowledge of coexisting properties consists in and his analysis of the scope of human knowledge as to these causal relationships, the argument on demonstrative knowledge of coexisting properties runs straight forward. This lack of demonstrative knowledge is expressed by Locke‘s assessment of contemporary knowledge of bodies as not being a science.<609> Below, we will see that two models has been proposed how to understand these causal relationships and the necessity of the necessary connections. I will argue for a different reading.

Aristotelians, as Locke conceives them, would present an alternative analysis, however. According to them, the possession of Aristotelian real essences justifies conclusions about the coexistence of properties. Aristotelians would contend that the real essence of a species of bodies, which is presumed to be common to all members, determines a set of features being shared by all specimens and not being (usually) contained in one‘s idea of the sort. Aristotelian real essences are thus conceived to justify the inclusion of properties (in one‘s idea of a sort) which one has discovered in a few specimens and thereby regard the idea to be a more complete depiction of the species.<610> As we have seen in connection with the fifth abuse of words,<611> Locke‘s response is to insist that the real essences of bodies are not precise, but prima facie specific, i. e. the specimens of a sort do not (necessarily) possess the same real essence.

Of course, from Locke‘s standpoint, he could refute the Aristotelian position also by


pointing out his conception of knowledge and claiming that a correct analysis of what knowledge of the coexistence of properties consists in reveals that the Aristotelian reasoning for the coexistence of properties is flawed and does not lead to the perception of the agreement of ideas. But this line of argument would seriously be undermined if Aristotelians could substantiate their view on real essences, since they could then call into question Locke‘s analysis of what knowledge of coexisting properties consists in. The reason is: Aristotelians believe that similarities on the explanatory level correspond to known similarities on the macrophysical stage, and they take this presumed correspondence to warrant the conclusion that all members of a sort possess a certain property even though one has experienced only some specimens to have the feature. Thus, according to the Aristotelians, one can know coexisting properties without knowledge of causal relationships and features in explanatory terms. As has been indicated, Locke objects against this view that microphysical resemblances need not, and in many cases do not, reflect macrophysical similarities.<612> Locke‘s account of real essences therefore paves the way for the claim that knowledge of coexisting properties affords knowledge of properties and causal relationships in terms of microphysical primary qualities.

The dispute over real essences is likewise the backdrop of Locke‘s extensive and separate discussion of our knowledge of coexisting properties in terms of the certainty and truth of universal propositions.<613> Locke alludes here to his analysis that, at his time, a name of bodies does not denote a species defined by an unknown (Aristotelian) real essence, but by a known nominal essence or respectively by the abstract idea signified by the term.<614> If words signified species characterized by unknown real essences, he argues, one would not only be ignorant of coexistent properties, but even of features defining a species. For one could not identify members of the sort, if kindship were defined by an unknown real essence. That is, if Aristotelians were right, one would not know any property which specimens have. This refutation of the Aristotelian conception of species and real essences secures on the one hand both that we can identify specimens and that we have


knowledge of features, namely of the properties which define sorts. On the other hand, however, the argument also establishes that we have hardly any knowledge of coexisting properties since one cannot conclude that all members of a sort have a certain property if the feature is discovered in some specimens.

The topic of real essences in this context is evidently manifest when Locke refutes the Aristotelian conception of species. But it is likewise present, even though less obviously, when he moves then on to insist lengthy for the rest of the chapter that knowledge of coexisting properties affords knowledge of necessary connections.<615> For the controversy on real essences makes plain: why in this context Locke repeatedly rejects the view that a feature can be known to be a coexistent property if it has been displayed by some specimens; and why he insists that knowledge of a feature truly going together constantly with the defining properties of a species affords knowledge that there really is a necessary connection. The backdrop of Locke‘s argument that only the perception of necessary connections yields knowledge of the coexistence of a property is again his contention that specimens can have and probably do have different real essences. For if the Aristotelian assumption of precise real essences were true, claims on coexistent properties could instead be justified even if one is ignorant of real essences, microphysical primary qualities and causal relationships.

In this context, the issue of real essences manifest in another way as well. Locke regards an explicit discussion of universal propositions (of coexistence) as necessary because people often raise knowledge claims in the course of their mistaking the meaning of universal propositions. The root of the misconception is that they do not understand names of bodies to stand for ideas, but for Aristotelian real essences.<616> Locke apparently alludes here to his analysis of the fifth abuse where he delineates different types of false knowledge claims and puts forward an account of why speakers are mistaken about the signification of their names of bodies.<617> Summing up, to grasp adequately Locke‘s argument on coexistence, one has to see its connections to his contention on real essences being not precise.


To return to the other three realms of knowledge, propositions of the first realm concerns the identity or diversity of entities, e. g. ’Gold is gold‘ and ’White is not black‘. Below, I will come back to our knowledge of these statements which effectively are set aside by Locke in his analysis of the extent of knowledge.<618> The third realm of relations does however not pertain to bodies. Strictly speaking, as Locke himself concedes, relations comprise not only what Locke explicitly calls relations, but also identiy, diversity and coexisting properties, since they all are states of affairs which are represented by, or correspond to, relations holding amongst ideas. Returning to the specific sense of relations which applies only to the third realm, Locke‘s paradigms for relations are triangles and their properties. Relations in this sense are simply defined as being relations in the general sense which are neither identities, nor diversities and nor coexistences of properties. And for Locke bodies do not possess any relations of this latter kind, but only relations in the sense of identities, diversities, and coexistences, since bodies qua bodies are understood as entities possessing only physical properties.

Finally, knowledge of real existence. In the chapter on the extent of knowledge, Locke is not very much concerned with knowledge of existence, e. g. ’There is a tree‘. But in the later chapter on knowledge of existant entities (except for oneself and God) Locke highlights knowledge of the existence of bodies in terms of sensitive knowledge. Present sensations yield sensitive knowledge of existing natural substances,<619> and (reliable) memories of past sensations establish knowledge that the depicted bodies had existed beforehand.<620> Thus, what Locke calls “experimental knowledge“ in connection with bodies in contrast to “universal knowledge“, is knowledge of the (past) existence of particulars and of their qualities, e. g. ’This piece of gold is fixed‘, which largely comprises remembered sensitive knowledge that depends on the individual and “collective“ memory of a subject respectively of society.<621> Moreover, since sensitive knowledge is about particular specimens, one has knowledge of the possession of properties solely with respect to particular specimens, for instance, that this piece of gold in front of me is


soluble in aqua regia. This means, other specimens might not possess this feature as well, e. g. one discovers another lump of gold to be not soluble in aqua regia.

This reasoning would of course be undermined again, if one assumes an Aristotelian conception of real essences, since it justifies the Aristotelians to conclude that all specimens have a certain feature if it was discovered in some members of a sort. Locke‘s argument on real essences and them being, in my words, prima facie specific thus purports correspondingly to his analysis of experimental and sensitive knowledge.

As we have seen, Locke maintains, there is only scanty intuitive and no demonstrative knowledge of coexisting properties. That is, we have hardly any universal knowledge of the possession of properties which are not defining a species. But we have sensitive knowledge of the existence of bodies and of their possession of properties not defining their species. That is, we do have plenty of knowledge, but it relates only to particular specimens. Due to our ignorance of real essences and causal relationships, one knows the possession of properties solely by the senses and only of particular specimens. As Locke puts it, we have no scientific, but only experimental knowledge of bodies.<622>

In addition to the assessment of knowledge as to the four realms, Locke also determines its extent as to kinds of bodies and properties which contemporary knowledge is about. First, in his account of the so-called ’causes of ignorance‘ he points to the limits of our sensual capacities to acquire ideas of properties, namely of secondary qualities.<623> Appealing to the existence of other spirits like angels having - of course - better discerning faculties than we have, Locke argues that one is ignorant of many sorts of properties which bodies possess. This ignorance is of a principle kind, since it is impossible for us to have ideas of features which do not affect our senses. Our sensual apparatus simply restraints the reception of ideas of secondary qualities. Thus, our knowledge of secondary qualities is fundamentally restricted because it reaches only as far as we can have ideas of qualities.

Second, in his account of the inadequacy of ideas, Locke makes plain that there is an incomprehensible high number of secondary qualities all of which we do not even come


close to know.<624> Third, Locke also emphasizes that we do not know the bodies existing somewhere in the universe.<625> Finally and most importantly, he points out the ignorance of microphyiscal bodies and properties.<626> This latter lack of knowledge is of course manifest in his analysis of the extent of knowledge, since it shows that the condition for demonstrative knowledge is not fulfilled.

Locke‘s accounts of the extent of knowledge as to the four realms and as to different types of bodies and properties clearly makes plain the limitation of knowledge as to its quantity. On this backdrop, Locke then assesses its “epistemic value“, namely to which extent it is real, instructive knowledge.

b. Real, Instructive Knowledge

It becomes manifests in various chapters that Locke is primarily, or even exclusively, interested in real, instructive knowledge.<627> In fact, as will now be delineated, Locke‘s verdict of contemporary knowledge being “very short and scanty“ refers to this kind of knowledge. Why is this so? and what is real, instructive knowledge?

The issue of the reality of knowledge is for Locke rather a pseudo problem. If knowledge is the perception of the (dis-) agreement of ideas, as Locke rhetorically questions his own depiction of knowledge, how do we know that it is real?<628> If knowledge is based on ideas and their connections, how can knowledge appropiately be about reality and does not concern only fantastical entities, e. g. that centaurs are not a harpy?<629> The point to note here is, as will be highlighted in what follows, that the reality of knowledge is understood in contrast to knowledge relating to fantastical ideas. The debate relates to knowledge about all kinds of entities, but as a matter of fact it focuses on substances, or respectively on bodies, since only ideas of them can genuinely be fantastical.<630> This apparently is the


reason why Locke introduces the issue with respect to ideas of substances.

According to Locke‘s account, knowledge is real, only if the ideas are real which make up a (mental) proposition.<631> This means for Locke, I maintain: knowledge is real, only if the ideas depict entities having the kind of relationship to reality that one intends the ideas to have when forming them. This is indicated by Locke‘s comparison of knowledge about fantastical entities with clear, sensation-like perceptions of entities as we have in dreams: in both cases our knowledge claims do not refer to entities in the appropriate way in order to be real knowledge.<632> I will not at length argue for this general understanding of Lockean real knowledge, but it applies in any case to bodies, since Locke clearly maintains that our knowledge of bodies is real only if our ideas of bodies are real, namely that they are copies of bodies existing in nature.<633> As Locke emphasizes, real knowledge of bodies is about a type of entities which once existed in the past and possibly exist again now or will in the future.<634> This means, we do have real knowledge of bodies, e. g. that gold is a metal and that gold is yellow, given that gold is defined as being yellow and by properties by which metal is defined as well.

At this point, Locke‘s distinction between trifling and instructive knowledge comes into play. The just mentioned kind of knowledge is trifling, since we know the respective propositions to be true simply in virtue of the fact that one idea includes the other one, e. g. the idea of gold contains the idea of yellow. One knows a trifling verbal proposition to be true solely by understanding the subject term and the predicate and realizing that the former includes the latter. By contrast, Locke calls knowledge instructive if, by and large, it is not trifling. More precisely, instructive knowledge is neither trifling nor about identities or diversities, nor about existence. On the face of it, Locke does not regard, for instance, knowledge of the following facts as instructive: that gold is gold, that gold is not silver, and that this piece of gold is fixed. This comprehension of instructive knowledge corresponds to Locke‘s contention that one hardly has any instructive knowledge of


bodies, a claim which otherwise would evidently be contradicted by one‘s (intuitive) knowledge of identities and diversities. As his examples indicate, instructive knowledge rather comprises (universal) knowledge of coexisting properties and relations.

Given Locke‘s assessment of contemporary knowledge as to bodies, it becomes plain that the judgement of it being “very short and scanty“ relates only to real, instructive knowledge. For one‘s universal knowledge of bodies virtually consists only in propositions which are already entailed by one‘s ideas of bodies. For example, if gold is defined as a yellow metal one knows that: gold is yellow, gold is a metal, gold is gold, gold is not silver, gold is not water etc. Evidently, this kind of knowledge is hardly worth mentioning it since it does not represent an advancement of knowledge which has any epistemic value. This is the reason why Locke virtually disregards it in his assessment of the extent of knowledge.<635> Thus, Locke‘s principal contention that contemporary knowledge of bodies is very short and scanty does not mean that there is hardly any kind of knowledge, but that there is hardly any knowledge of coexistence which is real and instructive. On the other hand, the kind of knowledge we do have according to him is not neglectable despite his strong rhetoric. After all, fundamental physical laws are deduced in connection with Locke‘s ordinary notion of body: to have figure entails the possession of extension, to pass on or receive motion by impulse supposes solidity, and to be both solid and in space implies the filling of space.<636>

In the light of what has been argued above, Locke‘s analysis of the extent of real, instructive knowledge of bodies depends heavily on his argument on real essences. For, if the Aristotelians were right, experimental knowledge could establish real, instructive knowledge of bodies. For instance, one‘s experience of pieces of gold being fixed would show that in general all gold is fixed. Without having established his views on real essences, Locke‘s reasoning would be exposed to Aristotelian attacks questioning his conception of instructive knowledge by insisting on a different account of what real essences are.

c. The Axiomatic Character of an Ideal Science of Bodies

Given the line of interpretation developed in previous chapters,<637> Locke‘s comments clearly imply that in an ideal science bodies are defined and understood in terms of real essences. Importantly, this depiction of real essences is manifest in two ways in Locke‘s account of knowledge as well. First, Locke justifies the possibility of attaining demonstrative knowledge in ethics<638> and explains our inability to achieve demonstrative knowledge of bodies<639> by the fact that in ethics the nominal essences of entities are also their real essences, respectively, that the nominal essences of bodies are not their real essences. Thus, there is a close nexus between the defining of species in terms of their real essences and achieving demonstrative knowledge.<640> On this backdrop, one naturally reads other passages, that depict the grasp of bodies in terms of real essences, as asserting an ideal for comprehending bodies in a scientific account,<641> namely that real essences comprise the microphysical properties of bodies in terms of which an ideal science classifies and depicts them.


Second, Locke conceives scientific research of coexistent properties as terminating in the attainment of adequate ideas, i. e. of ideas representing bodies by their real essences.<642> In other words, in an ideal classification or science, bodies are grouped together in species each of which is characterized by a real essence that is specific for the sort. Again, real essences comprise the properties in virtue of which a body is ideally grasped from a scientific viewpoint. And since ideas depict bodies by patterns having regularly been experienced, a real essence is understood to comprise features by which a body is ideally classified with respect to its similarities that it shares with other bodies on the explanatory stage. To be precise, in the light of Locke‘s comprehension of real essences in terms of primary qualities, the real essence of a body comprises the kind of explanatory features in terms of which one understands the body from a perception-neutral perspective.<643> Locke‘s account of knowledge therefore re-establishes what has been extensively argued in the context of archetypes, species, and essences.

Other commentators have also maintained that bodies are depicted and sorted by their real essences in an ideal account.<644> However, these interpretors neither draw the consequences for Locke‘s notion of real essences nor have they recognized the contradiction between this depiction of real essences and the concept of real essences which they ascribe to Locke as his official conception of real essences.

Importantly, an ideal account depicts bodies not only by their real essences, but enables to demonstrate, or respectively to deduct, the possession of properties. As delineated above, demonstrative knowledge is highlighted as the grasp of causal relationships holding between the defining properties of a species and an idea of a secondary quality, or alternatively, between the defining features and a microphysical property. This means, if bodies are defined by real essences, necessary connections between real essences and (the ideas of) properties of the micro- and macrophysical stage consist for Locke in causal relationships between real essences and (the ideas of) the features. That is, if one comes to


know of these causal relationships one has demonstrative knowledge of the coexistence of qualities with real essences. As delineated in the context of real essences,<645> these necessary connections correspond to the depend-on relationships holding between the real essences of bodies and their other features. Both relationships manifest the possession of coexisting properties. Given Locke‘s focus on knowledge of secondary qualities, an ideal science especially displays via demonstrations that the secondary qualities of bodies depend on, coexist or respectively are connected with their real essences in terms of which they are classified in species. This science of bodies would therefore be a deductive theory of bodies.

The question however is what is the precise nature of necessary connections as well as of their causal and deductive character. The dominant view is that, in some contexts, Locke operates with a quasi-geometrical model of necessary connections.<646> Locke is taken to believe that microphysical knowledge of real essences enables us, in principle, to deduce properties in the same way as one can in mathematics. To be precise, as Ayers contends, the difference between geometry and physics is that in physics the defining property of body to push other bodies out of its way is added to its geometrical figure.<647> This means, Locke claims that knowledge of real essences leads to quasi-geometrical, a priori knowledge. In this sense, Locke is called to be a ’pure mechanist‘.<648>

Commentators usually agree that this model applies at least to certain physical properties and their necessary connections to real essences, and most of them accept this model for all properties.<649> By comparison, Wilson agrees that this is Locke‘s official position, but insists that Locke‘s comments on superaddition reveal that in important cases causal relationships are also conceived as “God-forged“, e. g. in the case of gravitational forces and the interaction between mind and body. According to her, Locke contradicts himself


by maintaining two different models with respect to these physical relationships.<650> McCann, by contrast, agrees with Wilson on Lockean superaddition, but disagrees with her and Ayers that their textual evidence establishes that the quasi-geometrical model in also in place for gravitational forces and the causal relationship between mind and body.<651> He thus joins Wilson that in this latter context necessary connections add up to God-forged correlations between real essences and their dispositions to cause gravitation and thought.<652> For instance, the necessary connections between real essences and secondary qualities are God-forged causal relationships between real essences and ideas of secondary qualities which God has simply ordained by law and which do not consist in an ordinary physical relationship involving physical processes. There is nothing more to say than that the causal relationship holds due to a devine act of correlating mind and body.<653> McCann attempts to reconcile this view with Locke‘s notion of knowledge by conceiving these God-forged correlations as necessary connections which one can grasp with the help of God, namely when God informs us that this and that correlation holds by an act of devine revelation.<654>

Below, I will discuss the issue of superaddition. In particular, McCann‘s own textual evidence will be re-interpreted where he sees Locke to distinguish between physical and mathematical demonstrations in a way that allows him to understand Locke as coherently maintaining two distinct models, namely that the former are God-forged connections and the latter conceptual ones.<655> Since I will join and reinforce Ayers‘s and Yolton‘s criticism against his and Wilson‘s approach of understanding Lockean superaddition, their reading of physical relationships as God-forged connections will not further be discussed here. So let us turn to the disputed passages which are quoted by Ayers and Wilson as displaying that Locke holds on to the quasi-geometrical model with


respect to secondary qualities. This line of interpretation is indeed tempting, but I will argue that this model is just the special case of a more general one.

To come to grips, one has first to emphasize that Locke conceives necessary connections to be physical, causal relationships. We have seen this above in the context of the extent of knowledge, but in this sense Locke also speaks of necessary connections when drawing analogies between mathematical and physical knowledge. A deduction of properties is said to afford ideas of “how those [sensible] Qualities flowed from [real Constitutions]“<656> and the internal constitution, or real essence, of a body is depicted as “the cause“<657> of the secondary qualities by which the body is defined as the member of a species. If necessary connections between physical properties were therefore understood to be on par with necessary connections between mathematical properties, namely to be conceptual-like relationships, Locke would maintain that the discovery of causal relationships is done by discerning conceptual relationships. As just indicated, according to Ayers, quasi-geometrical physical relationships are obtained by adding the defining property of body to push other bodies out of its way to its geometrical figure.<658> That is, reflection on the figure of bodies in conjunction with their specific capacity to push other bodies out of their way is supposed to lead to insights into their causal interactions.

By comparison, I contend, Locke believes that insight into causal interactions leads to a conceptual understanding of bodies, their constitutions and interactions which subsequently enables one to find proofs and to attain thus demonstrative knowledge of coexisting properties. That is, an acquired empirical comprehension of bodies leads to a conceptual understanding that allows in a second step to deduce properties in a mathematical style. And a thorough grasp of bodies, their microphysical properties and causal operations is the basis for a comprehensive axiomatic theory of bodies. As we will see, for Locke a partial understanding of the causal powers of bodies allows already some deductions. In this sense, I contend, an ideal science of bodies is for Locke an empirical, comprehensive, true axiomatic account. Thus, contradicting the orthodox view, a grasp of only the real essences of bodies, but not of their causal interaction as well, does not enable


one to discover conceptual-like relationships of (all) their properties.

I will first discuss the controversial passages and come then back to the view I ascribe to Locke. The point I first want to make is that the less important passages rather support the here proposed view than the prevailing one. Take, for instance, the following reasoning:

“But such a complex Idea [scil. an everyday nominal essence] cannot be the real Essence of any Substance: for then the Properties we discover in that Body, would depend on that complex Idea and be deducible from it, and their necessary connexion with it be known; as all Properties of a Triangle depend on, and as far as they are discoverable, are deducible from the complex Idea of three Lines, including a Space.“<659>

Locke‘s argument against the claim that our common nominal essences are real essences implies only the contention that the deduction of properties from a real essence implies knowledge of necessary connections. The passage does not entail that the comparison between the deduction of physical properties and the deduction of mathematical properties implies that the physical features are deduced by discerning conceptual-like relationships only on the basis of knowledge of the real essences of bodies. Instead, Locke‘s comments on the conditions for demonstrative knowledge of coexisting non-sensible secondary qualities apparently support the here advanced interpretation:

“§11. Had we such Ideas of Substances, as to know what real Constitutions produce those sensible Qualities we find in them, and how those Qualities flowed from thence, we could, by the specifick Ideas of their real Essences in our Minds, more certainly find out their Properties, and discover what Qualities they had, or had not, than we know by our Senses: and to know the Properties of Gold, it would be no more necessary, that Gold should exist, and that we should make Experiments upon it, than it is necessary for the knowing the Properties of a Triangle, that a Triangle should exist in Matter, the Idea in our Minds would serve for the one as well as the other.“<660>

The punchline is: when Locke insists that a deduction of properties is said to afford ideas of “how those [sensible] Qualities flowed from [real Constitutions]“,<661> he already presupposes our attainment of knowledge of sense perception, namely of “how those


[sensible] Qualities flowed from [real Constitutions]“ or respectively of how bodies operate on our senses. This lends credibility to the here proposed reading: in general, demonstrative knowledge of necessary connections affords, is based on, and consists in microphysical knowledge of bodies and their causal interaction. Consider, moreover, the next passage:

“§16. But as to the Powers of Substances to change the sensible Qualities of other Bodies, which make a great part of our Enquiries about them, and is no inconsiderable branch of our Knowledge; I doubt, as to these, whether our Knowledge reaches much farther than our Experience; or whether we can come to the discovery of most of these Powers, and be certain that they are in any Subject by the connexion with any of those Ideas, which to us makes its Essence. Because the Active and Passive Powers of Bodies, and their ways of operating, consisting in a texture and motion of Parts, which we cannot by any means come to discover: ‘Tis but in very few Cases, we can be able to perceive their dependence on, or repugnance to any of those Ideas, which make our complex one of that sort of Things.“<662>

Here Locke links the attainment of demonstrative knowledge of coexisting qualities with the discovery of “the Active and Passive Powers of Bodies, and their ways of operating“ in terms of the “texture and motion of Parts, which we cannot by any means come to discover.“ In other words, Locke speaks of the necessity to come to know of physical facts, but not of conceptual relationships holding between ideas. And, decisively, these facts do not concern only real essences, but their causal interaction as well. On the other hand, turning now to the most important passage on this issue, there seems to be strong support for the quasi-geometrical model when Locke declares:

“I doubt not but if we could discover the Figure, Size, Texture, and Motion of the minute Constituent parts of any two Bodies, we should know without Trial several of their Operations one upon another, as we do now the Properties of a Square, or a Triangle. Did we know the Mechanical affections of the Particles of Rhubarb, Hemlock, Opium, and a Man, as a Watchmaker does those of a Watch, whereby it performs its Operations, and of a File which by rubbing on them will alter the Figure of any of the Wheels, we should be able to tell before Hand, that Rhubarb will purge, Hemlock kill, and Opium make a Man sleep; as well as a Watch-maker can, that a little piece of Paper laid on the Balance, will keep the Watch from going, till it be removed; or that some small part of it, being rubb‘d by a File, the Machin


would quite lose its Motion, and the Watch go no more. The dissolving of Silver in aqua fortis, and Gold in aqua Regia, and not vice versa, would be then, perhaps, no more difficult to know, than it is to a Smith to understand, why the turning of one Key will open a Lock, and not the turning of another.“<663>

Given that Locke does not mean God-forged connections, the operations Locke speaks here of are physical processes and causal relationships in the ordinary sense. This means, Locke‘s necessary connections between the properties of bodies are again conceived as consisting in physical processes or causal relationships respectively. Now, the crucial question of interpretation relates to Locke‘s two comparisons, namely between knowledge of coexistent secondary qualities, on the one hand, and on the other hand, knowledge which a watch-maker or a smith has and respectively knowledge in mathematics. Locke seems to assert that knowledge of the microphysical configuration of bodies is sufficient to discover how bodies interact and thus which properties coexist with their real essences, just as we are able to deduce mathematical properties from the real essence of a triangle or just as we know that a key turns a lock if one knows that the shape of the key fits the lock.

To come to grips with the passage, one has first to distinguish between two important claims Locke raises here. First, knowledge of the internal constitutions of two bodies entails knowledge of how they interact. Second, deduction of the latter kind of knowledge is like the knowledge a smith or watch-maker has. The key to understand aright both contentions lies in Locke‘s assertion that knowledge of the internal constitution of two bodies enables one to deduce several of their operations one upon another. That is, Locke does not contend that knowledge of real essences is the basis for deducing all features coexisting with the real essences. Moreover, in this sense one naturally reads Locke also as to our macrophysical knowledge of the causal powers of bodies. For instance, to say that a key has the capacity to turn a lock, implies that the key is turned with enough force to move the corresponding part of the lock if the key is turned. Thus, to know in advance for each degree of force, or impulse respectively, whether the key will turn, one has to understand how impulse works. In other words, knowledge of causal interaction always involves an understanding of impulse whether on the micro. or macrophysical stage. Even if a key is turned with enough force, it passes on impulse to the corresponding parts


of the lock. Similarly, how can a watch-maker know for every stone beforehand whether the stone will stop or be crumbled by the famous clock of Strasbourg if it is placed between the wheels of its mechanical set-up? To know that, one would have to understand not only impulse, but the coherence of matter as well. But Locke points out that we are ignorant of both. We do not even have a conception of how impulse operates and what coherence consists in. These considerations rather make one doubt how Locke can maintain in the first place that a watch-maker and a smith have knowledge of this kind of macrophysical capacities of bodies. Yet, Locke clearly asserts this.

First of all, it seems to me, Locke is not aware of the predicament for otherwise he would have said more and would not have simply drawn the analogy. He apparently believes and appeals to the intuition that one can have this kind of a priori macrophysical knowledge. And this intuition can be squared with his official notion of knowledge, I will now argue. The point is to understand the macrophysical knowledge claims appropriately. Take, for instance, a mill stone. Our conception of a mill stone may be that it is part of a certain mechanism and that it thus has the power to grind corn. If this is so, one a priori knows that mill stones grind corn. It is a conceptual truth. Crucially, Locke‘s comments show that something similar applies to our concept of body, impulse, and the coherence of bodies:

“§13. That the size, figure, and motion of one Body should cause a change in the size, figure, and motion of another Body, is not beyond our Conception; the separation of the Parts of one Body, upon the intrusion of another; and the change from rest to motion, upon impulse; these, and the like, seem to us have some connexion one with another. And if we knew these primary Qualities of Bodies, we might have reason to hope, we might be able to know a great deal more of these Operations of them upon another: But our Minds not being able to discover any connexion betwixt these primary qualities of Bodies, and the sensations that are produced in us by them, we can never be able to establish certain and undoubted Rules of the Consequence or Co-existence of any secondary Qualities, though we could discover the size, figure, or motion of those invisible Parts, which immediately produce them.“<664>

Locke contends that we conceive some connections between the relevant properties in causal interaction. That is, we have some understanding of causal processes, namely of


“the separation of the Parts of one Body, upon the intrusion of another“, of “the change from rest to motion, upon impulse“ and that “the size, figure, and motion of one Body should cause a change in the size, figure, and motion of another Body“. In short, according to Locke one has a deficient, but notwithstanding basic grasp of mechanical interaction.

Of course, this elementary understanding is for Locke acquired by experience. And only further experience of microphysical properties can enhance this comprehension of the causal relationships. Importantly, this claim differs from Locke‘s contentions that figure entails extension, that receiving or passing on of motion by impulse supposes solidity, and that being solid and in space implies the filling of space.<665> In the light of Locke‘s notion of knowledge, he clearly takes these propositions for conceptual truths. The reason is that our experience of causality which is entailed in our concepts implies these conceptual truths. But this is not the case regarding the details of mechanical interactions. Accordingly, we cannot deduce coexisting properties from the defining features of body or of our species of bodies.

Moreover, this limited, but fundamental comprehension of causality has somehow to be cashed out. I thus interpret Locke to maintain that our everyday grasp of the mechanical, causal capacities of bodies is derived from our everyday experience of these interactions. If this is so, there must be some conceptual truths regarding bodies and their interactions, e. g. that a key with an appropriate shape and being turned with an adequate force opens a lock. This kind of knowledge of the causal powers of bodies has to be part of our understanding of them, otherwise we would not know what it means that, for instance, they can push each other out of their way under appropriate circumstances! This comprehension of impulse, coherence, intrusion, and the like is rather sketchy. But it entails knowledge of the behaviour of bodies in the easy cases. Correspondingly, knowledge of internal constitutions leads to a priori knowledge of several of the operations of bodies.

According to this reading, in the context of bodies Locke‘s necessary connections are causal


connections. And the kind of necessity of the connection is causal or physical necessity, i. e. the necessity of natural law. Consequently, one acquires knowledge of these necessary connections by attaining knowledge of causal relationships.

An ideal science of bodies thus is an axiomatic, empirical account of bodies, their properties, and caual interactions. This axiomatic theory has to be true and comprehensive since it is depicted as enabling us to find proofs regarding all coexisting properties. In other words, such an axiomatic, empirical theory is an ideal scientific account of bodies. This axiomatic character is manifest when Locke contends that knowledge of the real essences of bodies and of their operations would make experiments superfluous since one then could deduce properties as in mathematics.<666>

“§11. Had we such Ideas of Substances, as to know what real Constitutions produce those sensible Qualities we find in them, and how those Qualities flowed from thence, we could, by the specifick Ideas of their real Essences in our Minds, more certainly find out their Properties, and discover what Qualities they had, or had not, than we know by our Senses: and to know the Properties of Gold, it would be no more necessary, that Gold should exist, and that we should make Experiments upon it, than it is necessary for the knowing the Properties of a Triangle, that a Triangle should exist in Matter, the Idea in our Minds would serve for the one as well as the other.“<667>

Furthermore, Locke also points out that a full grasp of secondary qualities and of all the circumstances conditioning the possession of them amounts to nothing less than a comprehensive understanding of matter, namely of “all the Effects of Matter, under its divers modifications of Bulk, Figure, Cohesion of Parts, Motion, and Rest“.<668> And since necessary connections qua causal interactions involve impulse and, in some cases at least, the coherence of corpuscles, Locke contends in a similar passage that a thorough grasp of the coexistence of features affords knowledge of “the coherence and continuity of the parts of Matter“ and “the original Rules and Communication of Motion“.<669> It seems to me, Locke is clearly aware of the implications of his conception of knowledge regarding bodies.


But we are far from having such an ideal understanding because we know neither the microphysical properties of macrophysical bodies nor the microphysical properties of microphysical bodies, e. g. of minute bodies that are part of the causal interaction between our senses and macrophysical bodies and the causal relationships between bodies.<670> In other words, due to our lack of microphysical knowledge, i. e. knowledge of minute bodies transmitting motion from body to body, of the coherence of corpuscles, and of secondary qualities in terms of microphysical primary qualities, we are ignorant of coexisting properties since we do not conceive the necessary connections holding between a feature and the defining properties of a species.

On this backdrop, Locke is apparently aware of the cardinal problem which the axiomatic character imposes on a science of bodies, namely the question of its material adequacy. In fact, this is the issue of Locke‘s discussion of the reality of knowledge. As has been delineated above,<671> knowledge of bodies is real, if our ideas are copies of bodies existing in the world. Real knowledge of bodies is only about entities which once existed and for which it is therefore possible to exist (again) in nature. Given this conception of real knowledge, it naturally applies to all aspects which a theory of bodies comprises, e. g. causal relationships. In this sense, Locke‘s account of the reality of knowledge addresses the question of the material adequacy of an ideal, axiomatic theory of bodies.

However, Locke is not fully aware of the significant problem in virtue of which criteria one knows that a theory truly is materially adequate. As I will indicate at the end of the chapter, I believe the root of this is Locke‘s pessimistic outlook on achieving significant progress of knowledge. Let it be as it may, Locke has a rather naive view on how we can recognize that we truly have ideal ideas of microphysical properties and of causal interactions. He apparently comprehends our acquisition of ideal ideas in terms of ideas being conveyed by microscopes and thereby conceives microscopes simply as a “technical extension“ of our natural epistemic faculties, i. e. of our senses, since he speaks of “microscopical eyes“ perceiving microphysical structures.<672> And given furthermore that


sensations under ideal conditions serve for him as the paradigm for knowledge,<673> knowledge of microphysical features and of causal interactions appears to be undramatic, namely as being achieved by technically enhanced sensations under appropriate conditions of perceptions. Locke therefore substantantially underestimates the problem when we know that our grasp of bodies is comprehensive, e. g., in modern terms, which elementary particles are really the most basic ones. To put it in another perspective, Locke does not really tell us when experimental research comes to an end and when the development of an axiomatic ideal account of our results and the search for demonstrations begin.

This kind of naivity ties in with Locke‘s conception of simple ideas. As Krüger has pointed out,<674> one fundamental problem of simple ideas is that Locke conceives them as the elementary compounds of cognitive content which one cannot further differentiate. This, however, is simply not true. One can always go on to distinguish between two colours. At least in the case of our everyday range of colours, one can always draw finer distinctions. Locke apparently attempts to solve this problem by introducing the so-called simple modes, e. g. shades of colours, but unsucceessfully.

The upshot is a partial re-positioning of Locke‘s place in the history of philosophy. In rough and ready terms, Locke‘s conception of an ideal account of bodies is substantially farer away from Descartes‘s rationalism and closer to Hume‘s empiricism than is usually thought. The problem with Locke‘s conception is not that it has a Cartesian, mathematical-like a priori character, but that Locke is rather naive on the question of its material adequacy.

A final remark as to the scope of such an ideal account of bodies. As we have seen, ideas of bodies genuinely serve the epistemic purpose to sort and depict bodies by similarities being regularly displayed in nature. This means for Locke, of course, that classification concerns, in principle, all the (secondary) qualities which bodies possess.<675> And it likewise naturally relates to all bodies irrespective of where they exist, on Earth or elsewhere in the universe, and irrespective of whether they are of a macro- or


microphysical size.<676>

d. Remedies to Advance Contemporary Knowledge of Bodies

On the backdrop of Locke‘s view of an ideal science of bodies, his analysis as to the extent of contemporary real, instructive knowledge becomes even more disillusioning. One does not only have hardly any instructive, real knowledge, but one is also miles away from an ideal science of bodies, since one is ignorant of microphysical properties, namely of real essences, matter, and causal connections. Not surprisingly therefore, Locke proposes remedies to advance contemporary knowledge which adds up to a conception of a contemporary science of bodies that takes into account prevailing ignorance.

Given the attested ignorance of microphysical properties, Locke develops, consequently, a conception of a contemporary science in the light of his general claim that: ideas of bodies stand in the perspective of the epistemic project to depict bodies by their similarities on the macrophysical level as a substitution for a portrayal by their microphysical resemblances. More specifically, Locke concludes in the chapter on the improvement of knowledge that one has to conduct experiments to discover similarities and gather their results systematically. The scientific community, so to speak, should compile their observations in a so-called natural history of bodies.<677> This process is likewise depicted as making our ideas of bodies more perfect, complete or adequate, i. e. one forms ideas which include larger sets of properties.<678> For example, if experiments reveal that various parcels of gold share further properties being not contained in the idea of gold, one would have to generate an idea which also includes the new, found features. In this sense, the former idea is enlarged and it depicts its specimens more adequately or perfect, namely by more properties they share. And if some parcels of gold display a quality which other ones do not, one would have to differentiate the old idea into two ideas portraying two similar, but different sorts of substances. For instance, one idea represents gold that is fixed,


whereas another one depicts gold that is not fixed. Progress of knowledge therefore consists in the genesis of ideas portraying classes of bodies by as many features as possible, which they recurrently share. This leads to the specification of ideas and differentiation of species.

Locke also suggests the development of a nomenclature, i. e. a well defined and generally used set of names of species. In other words, Locke appeals here to his ideal for communication and demands that scientists use their words with the same, uniform, and generally known signification. This becomes plain in his account of the imperfections of words where this use is proposed as a measurement to achieve an unequivocal vocabular in natural philosophy to avoid confusion that arises because speakers signify different ideas with the same name.<679> Locke is thereby aware of the fact that one can hardly install a well defined and generally used vocabulary at the conference table. Yet, he insists, this ideal remains to be realized as far as possible by scientists and in their communication. Summing up, Locke suggests the development of a nomenclature classifying bodies in species as specific as experiments reveal.

What about other means to enhance knowledge?<680> In discussing, mathematics and a future science of ethics, Locke proposes to advance knowledge by finding new demonstrations, i. e. chains of intermediate ideas linking two ideas making up a proposition.<681> This “method of demonstration“, however, is not recommended for bodies. The reason becomes obvious in the light of Locke‘s account of the prospects of enhancing human knowledge of bodies, as delineated below:<682> According to him, there is virtually no hope to achieve demonstrative knowledge. Given these bleak prospects, there is no place for methods to gain knowledge by discovering demonstrations. The method of demonstration thus applies only to an ideal or nearly ideal science of bodies


which is out of reach on Locke‘s account.

However, besides his two official ways to advance human knowledge, namely natural history and demonstrations, there are also hints that the use of hypotheses can serve as a third method. Laurens Laudan has opened a debate with his claim that Locke, allegedly, recognizes the importance of employing hypotheses in discovering new truths.<683> Laudan is right that in some passages Locke does claim that hypotheses can enlarge our understanding. For instance, Locke does maintain that hypotheses “are at least great helps to the memory and often direct us to new discoveries“.<684> But if one reads the quote in context, its message is less ambituous as it first seems:

“§13. Not that we may not, to explain any Ph_nomena of Nature, make use of any probable Hypothesis whatsoever: Hypotheses, if they are well made, are at least great helps to the memory and often direct us to new discoveries. But my Meaning is, that we should not take up any one too hastily, (which the Mind, that would always penetrate into the Causes of Things, and have Principles to rest on, is very apt to do,) till we have very well examined Particulars, and made several Experiments, in that thing which we would explain by our Hypothesis, and see whether it will agree to them all; [...] And at least, we take care, that the Name of Principles deceive us not, nor impose on us, by making us receive that for an unquestionable Truth, which is really, at best, but a very doubtful conjecture, such as are most (I had almost said all) of the Hypotheses in natural Philosophy.“<685>

What is Locke‘s position? First, since Locke speaks of the human mind as “[penetrating] into the Causes of Things“, he really refers to explanatory theories and not merely to empirical generalizations, e. g. gold is fixed. Second, Locke clearly distinguishes here between useful hypotheses and mere conjectures. Third, according to him, there are only very few useful hypotheses. Since Locke is explicitly favourable only to Boyle‘s corpuscularian theory and Newton‘s principle of gravitation,<686> he probably had these in


mind.<687> Fourth and importantly, this whole passage is a concession, since in the preceding paragraphs he criticizes people for raising false knowledge claims as to spirits claims on the basis of not well founded hypotheses. And, more important, in the subsequent paragraph Locke then mentions “ways to enlarge our Knowledge“ in natural philosphy which do not include the use of hypotheses.<688> Thus, Locke does concede that hypotheses can enlarge knowledge, (if they are well founded on careful observation and experiment,) but apparently neither very much and nor in a systematic way. In the light of Locke‘s account, there seems to be no ground for assuming that for him the use of hypotheses is a genuine tool for discovery. I therefore believe, hypotheses can be useful for Locke only in the sense that they give a general, though hypothetical, understanding of bodies at hand, which promotes experiments and thus discoveries. Not more, but not less either. This corresponds to Locke‘s praise of Newton‘s principle in the Conduct as “the basis of natural philosophy“.<689>

What about induction? As we have seen, Locke‘s natural history is based on systematically collected results of carefully conducted experiments. The reconstruction of Locke‘s doctrine of real essences showed however that he emphasizes the gap between knowledge and probability, natural history and hypothetical generalizations.<690> The goal of natural history is to compile experimental findings to make one‘s ideas as adequate as possible, i. e. to expound a nomenclature depicting species of bodies as precisely as possible. We thus advance our knowledge by enlarging our conceptual understanding by forming concepts which depict classes of bodies by as many properties as possible. And Locke contrasts this kind of knowledge with alleged knowledge claims about coexisting properties which are only warranted by experience. For instance, given that gold is not defined by being soluble in aqua regia and given further that we do not have any proof demonstrating the coexisting of this property with the defining features of gold: one would still not know whether gold is soluble in aqua regia, even if experiments show that


all known parcels of gold are soluble in aqua regia. Locke can justify this position in two ways. First, one knows coexistence only if one perceives the agreement of the respective ideas; experiments cannot produce knowledge in the required sense. Second, the (nominal) essences of our ordinary species are made by men, not by nature for which reason it is epistemically possible that there is a parcel of gold not possessing a certain property which is not soluble in aqua regia.<691>

To sum up. pace other commentators, who rather downplay Locke‘s remarks on hypotheses, I therefore count natural history and, to some degree, the use of hypotheses as Lockean methods of discovery.<692> They are, so to speak, his “positive“ means to enhance knowledge. Other comments entail moreover a “negative“ measurement, namely the abandonment of the abuse of language.

In his chapter on maxims, Locke denounces the belief that maxims are steps to improve knowledge. As previously delineated,<693> maxims are very general, intuitively known propositions having been regarded as principles to prove other propositions. Locke concedes that our grasp of maxims is proper knowledge since they can be known intuitively. Yet, he points out, maxims do not help to advance knowledge, since the kind of propositions which they are supposed to prove are grasped independently of maxims. The reason simply is that the propositions in question can likewise be known intuitively. Quite the contrary, the belief in maxims rather confuses and leads to alleged knowledge claims hindering the progress of knowledge. In this context, Locke discloses the Cartesian conception of body as being based on an abuse of language and thus refuses the basis for a Cartesian science of body.<694>

Not less importantly, throughout the Essay, Locke denounces repeatedly the Aristotelian use of language and corresponding theories of bodies as the hindrances of the progress of knowledge.<695> Locke regards this abuse of language, I argued, as the source of a fundamental misconception of what real essences and our common species of bodies


are.<696> According to him, one assumes members of an everyday sort to share a common, but unknown real essence which comprises all microphysical resemblances that are classificatorily relevant. This real essence is specific for all specimens of a sort and distinguishes them from all other species. As a consequence, one abuses language by taking names of bodies not to stand for the ideas one has, but for unknown real essences. One thus beliefs to be able to discuss which set of features is the true real essence of a sort, e. g. what the genuine real essence of human beings is. These speakers moreover conceive the joining of further properties to an idea as making one‘s ideas more complete or perfect, i. e. as representing the alleged real-essence species by a larger set of properties. In general, laymen have this understanding. But Aristotelians share this comprehension too and go even further by developing a more specific, but unintelligible conception of species and real essences, namely their theory of forms. To abandon the Aristotelian abuse of language would therefore advance knowledge in the sense that it “[removes] some of the Rubbish, that lies in the way to Knowledge“.<697>

Hence, to abandon the use of maxims and the abuses of language advances knowledge because it leads to the abandonment of Aristotelian and Cartesian misconceptions of a science of bodies.<698> Correspondingly, Locke‘s account of remedies is effectively the suggestion of an alternative, corpuscularian conception of a science of bodies. Maxims are replaced by experiments and observation, whose results are systematically compiled, as means to enhance knowledge. A corpuscularian understanding of real essences, species, and classification is substituted for an Aristotelian one. Locke‘s analysis therefore adds up to an assessment of which scientific programme current at his time is the appropiate one. (Besides the Cartesian, Aristotelian, and Boylean accounts of bodies the alchemists proposed another one; but Locke hardly ever referred to them,<699> maybe because he thought Boyle had already successfully dealt with them.) And we have seen, one substantial issue underlying the debate is what a correct conception of real essences consists in. For, if the Aristotelian idea that real essences are precise were true, not only


Locke‘s theory of species and classification would seriously be undermined, but also his major contention on experimental knowledge that findings of new properties as to some specimens do not justify the conclusion that all specimens possess the features.<700>

e. Prospects of Advancing Knowledge

The delineated scientific programme of course pertains only to the advancement of contemporary knowledge. If one had microphysical knowledge of matter, real essences, and causal interactions, one could enhance knowledge only by discovering demonstrations establishing, for example, coexistent properties. But what are the prospects of acquiring one day such an ideal comprehension of bodies? Locke is extremely pessimistic. For besides his disillusioning stock-taking he moreover raises principal concerns over achieving a comprehensive understanding of bodies and their properties. This concerns five aspects of what needs to be known for an ideal science which differ in the difficulty of discovering them: real essences, matter, causal interactions amongst bodies, all the circumstances causally determining a property, and the relationship between bodies and the human mind.

First, Locke is pessimistic about our discovery of real essences since, apparently, it seems to him too difficult to construct instruments aquivalent to “microscopical eyes“,<701> i. e. microscopes of a far higher resolution.<702> But, according to him, we do have at least a general corpuscularian conception of what real essences are, namely of real essences being microphysical structures consisting of cohering corpuscles. Yet, even on the presumption of the corpuscularian model for real essences, one does not have a comprehension of how to highlight in principle a particular quality in terms of a specific “combination“ of microphysical primary qualities.<703> That is, corpuscularian theory is not specific enough to determine the corresponding microphysical features for a given quality.

Second, in the case of the substratum of bodies, we even lack an adequate conception. As


has been indicated in the second chapter,<704> Locke rejects all contemporary approaches to explain the cohesion of corpuscles and the transmission of impulse. For him, one does not have an idea of how to explain these mechanisms. Similarly, according to Locke one does not have any idea of how to explain the phenomenon of gravitation.<705> On the other hand, this account implies that one does have a partial, though inadequate, conception of matter, namely as a stuff consisting of cohering, solid, and mobile corpuscles whose coherence, mobility and gravitational forces cannot be understood. As Locke puts it, “we have no Idea of what it is, but only a confused obscure one of what it does“.<706>

Third, this latter ignorance is effectively paired with the former one as to how bodies operate upon each other, since causal interaction amongst bodies involves impulse, if not cohesion as well, and microphysical features which pass on and receive motion. Perhaps not surprisingly, Locke maintains that it probably needs devine revelation to understand this kind of causal relationships or respectively the powers of bodies to act upon each other.<707>

Fourth, this ignorance is part and parcel of a deeper one. As Locke insists, a comprehensive grasp of a property is virtually impossible because it includes knowledge of all the relevant circumstances causally determining the possession of a property.<708> Usually, Locke points out, one conceives a body and its properties as being isolated and solely as to its own constitution; one does not take into account that other bodies determine a body‘s properties as well. But to conceive thoroughly the feature of being alive, he insists, one has to understand not only the internal constitution, i. e. the microphysical mechanism, of animals and plants but also causal factors or properties of other bodies. For example, the sun has a great influence on life, since too much or not enough sunlight destroys life on earth. Who knows, Locke asks, whether a distant star does not condition life on earth? (This example relies of course on his assertion that one is ignorant of distant bodies and their causal interactions to bodies with our planet, but


the argument is generally related to the vastness of causal interactions among bodies and our ignorance of them.) Thus, for Locke it is virtually impossible to achieve a comprehensive understanding of properties, e. g. to be a living body, due to the complexity of causal interactions.

Finally, the discovery of the causal relationship between bodies and mind, e. g. sense perception, is for Locke even more doubtful, since we do not have any conception of the kind of relationship being involved. Since, as already pointed out, for Locke both materialism and dualism is possible,<709> it is reasonable to assume that for Locke one only knows that there are correlations between bodies affecting our senses and the appearance of sensations, but we are completely ignorant of what this causal relationship consists in.

However, several passages in which he expresses his pessimism about discovering the answer to the mind-body problem have recently stirred up an intensive debate. Margaret Wilson has opened the discussion by ascribing especially two claims to Locke.<710> First, thought cannot be explained by matter. Second, thought is rather supperadded to operations by God. Wilson does not highlight the latter assertion, but vigorously denies that she meant occasionalism.<711> At any rate, according to her, Locke holds that “mechanistic principles, or primary qualities, have limited explanatory power in Locke‘s considered view: the purposive action of an eternal thinking being is also required to account for phenomena“.<712> Thus, in some way or other, God has to play a role in explaining the relationship between thought and matter. Edwin McCann argues for the same position, except that, in contrast to Wilson, he attempts to reconcile the thesis on superaddition with Locke‘s mechanism.<713> McCann speaks of “God-forged connections“ between matter and thought, arbitrary laws ordained by God, which “salvage mechanism“.<714> In my eyes, Ayers and Yolton have convincingly shown the defects of this approach to understand Locke.<715> McCann has recently re-stated his position,


however.<716> It seems therefore to me appropriate to reconstruct carefully Locke‘s account by discussing the latest version of this line of interpretation. For instance, Locke argues:

“‘Tis evident that the bulk, figure, and motion of several Bodies about us, produce in us several Sensations, as of Colours, Sounds, Tastes, Smells, Pleasure and Pain, etc. These mechanical Affections of Bodies, having no affinity at all with those Ideas, they produce in us, (there being no conceivable connexion between any impulse of any sort of Body, and any perception of a Colour, or Smell, which we find in our Minds) we can have no distinct knowledge of such Operations beyond our Experience; and can reason no otherwise about them, than as effects produced by the appointment of an infinitely Wise Agent, which perfectly surpass our Comprehensions. As the Ideas of sensible secondary Qualities, which we have in our Minds, can, by us, be no way deduced from bodily Causes, nor any correspondence or connexion be found between them and those primary Qualities which (Experience shews us) produce them in us; so on the other side, the Operation of our Minds upon our Bodies is as unconceivable. How any thought should produce a motion in Body is as remote from the nature of our Ideas, as how any Body should produce any Thought in the Mind. That it is so, if Experience did not convince us, the Consideration of the Things themselves would never be able, in the last, to discover to us. These, and the like, though they have a constant and regular connexion, in the ordinary course of Things: yet that connexion to nothing else, but the arbitrary Determination of that All-wise Agent, who has made them to be, and to operate as they do, in a way wholly above our weak Understandings to conceive.“<717>

Let us start with the less controversial statements. First, Locke depicts the relationship between states of bodies and states of minds as a regular and even causal one, since according to him experience shows us that they “operate“ upon, or respectively “produce“, each other. Second, the way of how consciousness and body operate on each other is “unconceivable“ for us. Third, this inconceivability is explained by (the content of) the ideas one has. This latter point becomes plain in another passage which clearly includes all three statements:

“What certainty of Knowledge can any one have that some perceptions, such as v.g. pleasure and pain, should not be in some bodies themselves, after a certain manner modified and moved, as well as that they should be in an immaterial Substance, upon the Motion of the parts of Body: Body as far as we can conceive being able only to strike and affect body; and Motion, according to the utmost reach of our


Ideas, being able to produce nothing but Motion, so that when we allow it to produce pleasure and pain, or the Idea of a Colour or Sound, we are fain to quit our Reason, go beyond our Ideas, and attribute it wholly to the good Pleasure of our Maker. For since we must allow he has annexed Effects to Motion, which we can no way conceive Motion able to produce, what reason have we to conclude, that he could not order them as well to be produced in a Subject we cannot conceive the motion of Matter can any way operate upon?“<718>

Here, Locke justifies the possibility of both materialism and dualism by our lack of comprehending interaction between body and thought. More importantly, this ignorance is explained by our ideas, namely that according to our understanding of body and motion we cannot conceive how bodies interact on minds by motion. McCann, however, does not conclude from the passage that it is incomprehensible for us how they causally interact, but that they causally interact.<719> But this stronger interpretation is clearly not warranted by what Locke says. Quite the contrary, pointing out the inconceivability, does not mean for Locke that there is no causal connection between thought and body, since he insists instead that “we must allow he [scil. God] has annexed Effects to Motion, which we can no way conceive Motion able to produce“. He thus simply re-asserts his previous claim that we know this connection from experience. This is manifest in another passage as well:

“We are so far from knowing what figure, size, or motion of parts produce a yellow Colour, a sweet Taste, or a sharp Sound, that we can by no means conceive how any size, figure, or motion of any Particles, can possibly produce in us the Idea of any Colour, Taste, or Sound whatsoever; there is no conceivable connexion betwixt the one and the other.“<720>

Given Locke‘s assertion in the other quoted comments that there is a causal connection, he does not claim here that there is no connection because it is inconceivable, as McCann reads this passage again, but that the connection is inconceivable.<721> In the light of our experience and ideas, Locke maintains, we do know that there is causal interaction, but not what it consists in. Consequently, we have to understand Locke on this backdrop when he speaks of “superaddition“:


“We have the Ideas of Matter and Thinking, but possibly shall never be able to know, whether any mere material Being thinks, or no; it being impossible for us, by the contemplation of our own Ideas, without revelation, to discover, whether Omnipotency has not given to some Systems of Matter fitly disposed, a power to perceive and think, or else joined and fixed to Matter so disposed, a thinking immaterial Substance: It being, in respect of our Notions, not much more remote from our Comprehension to conceive, that GOD can, if he pleases, superadd to Matter a Faculty of Thinking, than that he should superadd to it another Substance, with a Faculty of Thinking; since we know not wherein Thinking consists, nor to what sort of Substances the Almighty has been pleased to give that Power, which cannot be in any created Being, but merely by the good pleasure and Bounty of the Creator.“<722>

Given what has been reconstructed so far, one should not read into Locke‘s talk of superaddition a mysterious or magic conception of (causal) relationship between body and thought and thus introduce incoherences into his account. As Ayers has already pointed out, Locke speaks of superaddition in other, definitely harmless contexts as well.<723> For example, mechanical properties of bodies are said to be superadded to matter by God.<724> It is therefore natural to conclude, as Ayers does, that Locke does not raise any stronger ontological claims than that God has the power to create the world in the way he pleases, thus determining whether dualism or materialism is true.<725> In all the so far quoted passages, Locke refers to God only as the being who establishes an unknown, for us inconceivable causal relationship. Consequently, the whole point of Locke‘s argument is an epistemological one: given our narrow understanding of the causal relationship between thought and body, both materialism and dualism is epistemically conceivable for us.

On this backdrop, one can naturally read Locke‘s reference to God, e. g.: “yet that connexion to nothing else, but the arbitrary Determination of that All-wise Agent, who has made them to be, and to operate as they do, in a way wholly above our weak Understandings to conceive.“<726> That is: even though we do not understand how mind


and body are causally interrelated, yet, one thing is for sure, the relationship is the one which God wanted it to be. Yet, as McCann rightly insists, if Locke really discusses only an epistemological issue, why does he refer to God in the first place?<727> It seems to me the deeper reason for Locke‘s referring in this context to God‘s power to create the world as he likes it, is that the matter at issue is a physical one. For, by contrast, God could not have ordained that the three angles of a triangle sum up to three right ones, since this would be a contradiction in terms. But our notions of matter and consciousness genuinely denote entities in the world whose constitution therefore depend on God‘s will.

This consideration appears to be manifest in another comment on our subject matter. Here Locke contrasts the inconceivability of triangles having not angles adding up to two right angles with our inconceivability of how body and thought interact. The mathematical state of affairs is inconceivable because one cannot conceive that the holding of the connection (between the idea of triangles and the idea of possessing angles being equal to two right ones) “depend[s] on any arbitrary Power, which of choice made it thus, or could make it otherwise.“<728> In other words, since not even God can establish a connection, the possibility that it holds is inconceivable. But the physical fact of how body and thought causally interact is inconceivable for us because “we cannot but ascribe [how they interact] to the arbitrary Will and good Pleasure of the Wise Architect.“<729> That is, since God has chosen to create the world as he wanted, it is inconceivable for us (with our ignorance of the subject matter) to determine the relationship without any further knowledge.

But given the incomprehensibility of the causal relationship, it becomes virtually impossible for Locke, in practical terms, to achieve knowledge of coexistent secondary qualities, since it consists of knowledge of the causal relationship holding between the microphysical primary qualities of bodies and our ideas of secondary qualities. We afford devine revelation.

To some up, besides the disenchanting stock-taking of the extent of contemporary knowledge of bodies, the outlook for advancement is gloomy. Locke seems to concede


that a classification of bodies in accordance to their real essences might be possible one day, but the attainment of real, instructive knowledge - not to speak of an axiomatic theory - is out of reach due to the incomprehensibility of causal relationships. In the light of these serious doubts about mankind developing an axiomatic theory, natural history appears not only to be a provisional conception for a science of bodies, but also to be an ever lasting one. On the other hand, since Locke expresses only reservations but neither presents nor hints at an argument why one should not be able to attain ideas of matter and real essences, or microphysical primary qualities respectively, he apparently does not maintain that we are neceassirily ignorant.

Moreover, as already alluded to,<730> there are for Locke further practical limitations to compile an adequate natural history. Besides the difficulty of establishing a uniform nomenclature,<731> the scope of discovery is restricted. First, he contends that the number of secondary qualities exceeds our cognitive capacity to know them all, since we cannot experience all the various dispositions a body has to interact with other bodies. Second, we do not achieve comprehensive knowledge even of those properties of which, in principle, we are capable to attain ideas as to our senses, since bodies and their features might be out of reach for our faculties, e. g. bodies and their properties somewhere in the universe. Thus, for Locke, any natural history will remain significantly incomplete even in respect of classifying bodies as to their properties on the observable level, not to speak of the microphysical stage.

This pessimistic outlook on the progress of knowledge in the perspective of an ideal account of bodies might be one reason why Locke‘s analysis does not discuss criteria determining which ideas depict real essences and causal relationships in terms of primary qualities. As argued above,<732> Locke apparently has a rather naive view on how we can recognize that we truly have ideal ideas of microphysical properties and of causal





652, IV.xiv.1; 644, IV.xii.9.


47, I.i.7.


543-53, IV.iii.8-21.


546, IV.iii.14; 123, II.iv.2. Cp. the chapter on solidity where Locke likewise contends that “[u]pon the Solidity of Bodies also depends their mutual Impulse, Resistance, and Protrusion“. Cp. 126, II.iv.5.


Cp. Ayers (1991), II, 149f.


546, IV.iii.14.


544f, IV.iii.11.


545, IV.iii.12.


545, IV.iii.13.


547, IV.iii.16.


547, IV.iii.16.


Cp. 545, IV.iii.13; 557, IV.iii.26; 558f, IV.iii.28.


556, IV.iii.25.


Cp. 10c.


As Goodin has recently pointed out, the topic of non-sensible qualities is usually neglected. Cp. Goodin (1992), 60. But even her very detailed account of the issue, with which I agree, overlooks this, at first sight, highly interesting claim of Locke that we possess knowledge of the coexistence or repugnance of this kind of properties.


381. II.xxxi.8.


545, IV.iii.13.


560, IV.iii.29.


Cp. 8c.


Cp. 8d.


Cp. 8d.




Cp. 6a-b.






Cp. 8.2.


Cp. 10b.


631-35, IV.xi.3-9.


636f, IV.xi.11.


582, Cp. 560, IV.iii.29.




553f, IV.iii.23.


381, II.xxxi.8.


554f, IV.iii.24.


555f, IV.iii.25


Cp. IV.iv, IV.v, IV.viii, and 602, IV.vii.11.


562, IV.iv.1.


563, IV.iv.1




565, IV.iv.6: “[...] because real Things are no farther concerned, nor intended to be meant by any such Propositions, than as Things really agree to those Archetypes in his Mind.“; 565, IV.iv.8: “[...] and to make our Knowledge real, it is requisite, that the Ideas answer their Archetypes.“; 568, IV.iv.11.


563, IV.iv.1f.


568, IV.iv.12.


568, IV.iv.12, and 578, IV.v.8.


543f, IV.iii.8.


546, IV.iii.14; 123, II.iv.2. Cp. the chapter on solidity where Locke likewise contends that “[u]pon the Solidity of Bodies also depends their mutual Impulse, Resistance, and Protrusion“. Cp. 126, II.iv.5.


Cp. 1b and 7.


643, IV.xii.7f: “This, I think, I may say, that if other Ideas, that are the real, as well as nominal Essences of their Species, were pursued in the way familiar to Mathematicians, they would carry our Thoughts farther, and with greater evidence and clearness, than possibly we are apt to imagine.“

§8. This gave me the confidence to advance that Conjecture, which I suggest, Chp. 3. viz. That Morality is capable of Demonstration, as well as Mathematics. For the Ideas that Ethicks are conversant about, being all real Essences, and such as, I imagine, have a discoverable connexion and agreement one with another; [...]“. Cp. 560, IV.iii.30; 565, IV.iv.7. Locke links here demonstrative knowledge to adequate ideas, i. e. to ideas portraying entities by their real essences.


644, IV.xii.9: “[...] We advance not here [scil. in our knowledge of substances, or of bodies respectively], as in the other (where our abstract Ideas are real as well as nominal Essences) by contemplating our Ideas, [...] Here we are to take a quite contrary Course, the want of Ideas of their real Essences sends us from own Thoughts, to the Things themselves, as they exist.“ Cp. 588,


Woolhouse draws the conclusion from these passages that knowledge of real essences is prerequisite for a priori knowledge. Cp. Woolhouse (1981), 144. In fact, he is of course referring to demonstrative knowledge, since according to Locke we have plenty of trifling a priori knowledge and few instructive a priori knowledge of bodies. But this claim seems to me too strong, since it is possible on Locke‘s position that we have demonstrative knowledge even if one is ignorant of real essences. Imagine, we discover that the idea of extension entails another idea. One could then demonstrate that figure entails this further property (of which this other idea is), given Locke‘s contention that figure presupposes extension.


In two passages, Locke links the possibility of having a science of bodies and scientific demonstrations with grasping bodies in terms of real essences. Cp. 644ff, IV.xii.9ff; 647, IV.xii.12.


648, IV.xii.14. In another passage, there is a nexus between scientific knowledge and adequate or respectively perfect ideas. Cp. 556f, IV.iii.26.


Cp. 3c and5b.


Cp. Ayers (1970), 39; Mackie (1975), 100. Yolton concedes that Locke‘s views entail that, in my words, an ideal science of bodies depicts them by real essences, but insists that Locke himself is not able to see this. Cp. Yolton (1970), 33.


Cp. 7a.


Cp. Ayers (1991), I, 102; Ayers (1991), II, 147; Krüger (1973), 243-46; Mackie (1975), 100-103; Wilson (1979), 143 and 147; Wilson (1982), 249; Woolhouse (1971), 19, 25, and 136.


Ayers (1991), II, 147.


Cp. Ayers (1991), II, 147 and 153; Mackie (1975), 102.


Cp. Ayers (1991), I, 102; Ayers (1991), II, 147; Krüger (1973), 243-46; Mackie (1975), 100-103; Woolhouse (1971), 19, 25, and 136.


Wilson (1982), 248f.


McCann (1985), 256ff.


McCann (1994), 71-75. McCann however disagrees with Wilson that Locke takes the cohesion of corpuscles to be God-forged as well. Cp. McCann (1994), 68f; Wilson (1982), 248.


McCann (1985), 254f. Cp. Wilson‘s denial that she wants to ascribe occasionalism to Locke. Cp. Wilson (1982), 249.


McCann (1985), 259; McCann (1994), 72.


I refer here to 559, IV.iii.29. Cp. McCann (1985), 258. Cp. 10e.




379, II.xxxi.6.


Ayers (1991), II, 147. Cp. also Ayers (1991), I, 102.


379f, II.xxxi.6.






547, IV.iii.16.


648, IV.xii.13.


545, IV.iii.13.


546, IV.iii.14; 123, II.iv.2. In the chapter on solidity, Locke likewise contends that “[u]pon the Solidity of Bodies also depends their mutual Impulse, Resistance, and Protrusion“. Cp. 126, II.iv.5.








559f, IV.iii.29.


558-60, IV.iii.28f. Cp. 554-57, IV.iii.24ff.


Cp. 10b.


303, II.xxiii.12.


Cp. 9d.


Krüger, (1973), 36-39.


This is manifest in his account of ideas of bodies being inadequate. Cp. 381, II.xxxi.8.


Cp. 555, IV.iii.24.


647, IV.xii.12. Cp. 520ff, III.xi.24f.


648, IV.xii.14.


509-12, III.xi.1-7. Cp. 8b.


Locke also discusses syllogisms, but critizies them as not genuinely enhancing knowledge. The reason is simple: one has first to understand a proof in terms of a chain of ideas in order to arrange it in form of a series of syllogisms. For Locke, a chain of ideas represents the “natural order“ of grasping facts showing another fact by a demonstration. Consequently, a proof consisting of syllogisms has to be re-arranged into a chain of ideas, if one wants to understand the proof. Cp. 672ff, IV.xvii.4.


649, IV.xii.15.


Cp. 10e.


Laudan (1967), 216f. Laudan argues specifically against Yost and his denial that Locke uses corpuscularian theory as a means for scientific discovery. Cp. Yost (1951).


Similarly, Locke maintains with respect to the probability of hypotheses on bodies which are constructed (and justified) by analogies: “This sort of probablility, which is the best conduct of rational experiments, and the rise of hypothesis has also its use and influence; and a wary reasoning from analogy leads us often into the discovery of truths and useful productions, which would otherwise be concealed.“ 666f, IV.xvi.12.


648, IV.xii.13.


Cp. 547f, IV.iii.16. Cp. Locke‘s Elements of Natural Philosophy:“It appears, as far as human observation reaches, to be a settled law of nature, that all bodies have a tendency, attraction, or gravitation towards one another.“ Cp. Works, III, 304.


Farr has pointed out that, according to Locke, hypotheses can also be useful in paractical terms. In particular, medical hypotheses can be useful as a rule of thumb to guide the physician. Cp. Farr (1987), 64.


648, IV.xii.14.


Works III, 282.


Cp. 10e. Cp. 582-85,


Cp. 7d.


Cp. Yolton (1970), 64-72, and 103, and Ayers (1991), I, 113-118.


Cp. 8b.


Cp. 8b.


Epistle, 10. 380, II.xxxi.6. 390f, II.xxxii.18. 404, III.ii.6. 417f, III.iii.17. 448f, 493ff, III.x.6-10. 502f, III.x.20f. 506, III.x.30. 509f, III.xi.3ff. 573, 580ff,


Cp. 8.2.


Epistle, 10.


Cp. 8b.


548, IV.iii.16.


Cp. 8c.


303, II.xxiii.12.






Cp. 2b.


Works, IV, 467f. Cp. Rogers (1978), 225f.


175, II.xiii.19.






Cp. 2a-b.


Wilson (1979), 144; Wilson (1982), 248f.


Wilson (1982), 248ff. Wilson rejects here Ayers‘s interpretation of her earlier article. Cp. Ayers (1981), 219.


Wilson (1982), 251.


McCann (1985), 243.


McCann (1994), 71 and 74f.


Ayers (1991), II, 144-53, 170, and 179-82; Yolton (1983), 14-28 and 198ff.


McCann (1994).


558f, IV.iii.28.


541, IV.iii.6.


McCann (1994), 69.


545, IV.iii.13.


McCann (1994), 70.


540f, IV.iii.6.


Ayers (1991b), 148.


Works IV, 460f.


Ayers (1991), II, 153.


558f, IV.iii.28.


McCann (1983), 247.


559, IV.iii.29.


560, IV.iii.29.


Cp. 10a.


Cp. 8b.


Cp. 10c.

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