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- 1 “Mr. Locke’s Reply to the Bishop of Worcester’s Answer to his Letter”, Works, 3: 97-184 (129). Stil (...)
1In his Answer to Locke of 1699, the Bishop of Worcester Edward Stillingfleet charged the Essay on Human Understanding gravely with encouraging “ill men” to take up the “new way of ideas” in order “to promote scepticism and infidelity, and to overthrow the mysteries of our faith”.1 The “new methods of certainty” inaugurated by Locke were apt “to leave men’s minds more doubtful than before,” and its consequences were expected to be dangerous in “an age wherein the mysteries of faith are so much exposed by the promoters of scepticism and infidelity” (Locke, Works 3: 140). In his reply to the Bishop, Locke rejected scepticism as “a pretty hard word” (156), but deferred consideration of it to another place: he preferred to deal with another criticism Stillingfleet had addressed to his Essay relating to a lack of distinction between nature and person, an error which could make Locke guilty of anti-trinitarianism. Some pages further down in the Reply, Locke attributed the imputation of scepticism to his “way of certainty by ideas” and his answer had a provocative tone: “to avoid scepticism, it is better to have some way of certainty (though it will not lead us to it in everything) than no way at all” (184). In other words, Stillingfleet’s criticism was intended only to conceal his inability to find a better way of certainty.
2Some months before, in his Letter to the Bishop, Locke had reacted more calmly and, in order to reaffirm the orthodoxy of his “new way of ideas” had firmly rejected the charge of speaking against the being of substances: any inference of their non-existence from the uncertainty and obscurity of their corporeal and spiritual notions was mistaken, since
a great many things may be and are granted to have a being, and be in nature, of which we have no ideas. For example; it cannot be doubted but there are distinct species of separate spirits, of which we have no distinct ideas at all: it cannot be questioned but spirits have way of communicating their thoughts and yet we have no idea of it at all. (Works 3: 18)
3Some years later, in his second Reply, Locke had to face the charge of scepticism again; in this circumstance, he interpreted it more as an objection to the small capacity attributed to knowledge by his way of ideas than as a refusal of its certainty. Stillingfleet had grounded his charge on Locke’s allowing, in the Essay, such a lack of adequate ideas and of connections between them and the things themselves (Works 3: 356), and Locke acknowledged this argument: “we are excluded from attaining any knowledge, as to the greatest part of the universe” (357); “we have no ideas of the mechanical affections of the minute particles of bodies, which hinders our certain knowledge of universal truths concerning natural bodies” (359). In Locke’s opinion, Stillingfleet’s inference from these premises was also correct (“since we can attain no science, as to body or spirits, our knowledge must be confined to a very narrow compass”), nonetheless he failed to appreciate it properly: “a little knowledge is still knowledge, and not scepticism.”
4Quite surprisingly, in writing to William Molyneux in 1697, Locke himself had brought the charge of scepticism against Stillingfleet: as a contender, the Bishop did not behave as one of “the few that have opinions, or at least seem, by their way of defending them, to be really persuaded of the opinions they profess”; this insincere attitude of his was a clear symptom of “scepticism, or at least want of concern for truth” (Correspondence 6, n. 2202, 22 February 1697).
5More cautiously, in his Essay (4.3.6, 543), Locke had labelled as sceptical and irrational any negation of the existence of that “something” in us “that thinks.” This disclaimer nonetheless had not preserved him from the charge of being sympathetic to this theologically dangerous position.
- 2 Cf. ECHU 4.3.29, 360: “The Things that, as far as our Observation reaches, we constantly find to pr (...)
6However, Locke’s insistence on human ignorance in the Essay was intended more as a means to lead men to recognize God’s wisdom than as a way to undermine reason’s attempts to acquire knowledge: although “the secret abstract nature of substance in general” is not attainable by our finite understanding, Locke affirmed that substances had to be considered an indispensable element in every sensible object, in order to properly use our rational faculties in the exploration of the visible, well-ordered parts of the universe (2.28.6). The perception of a rational order and harmony in nature was the main aim of experimental knowledge,2 whose limits, in Locke’s view, did not make the great design of which men are part less intelligible and reasonable.
- 3 This is always true in Locke’s works, since his Essays on the Law of Nature; in the Essay he writes (...)
7Taking for granted the existence of God,3 Locke could think the lack of ideas and the uncertainty of sensory information as utterly insignificant: it was "the Wisdom and the Goodness of the Soveraign Disposer of all things" (ECHU 2.7.6) that guaranteed the proper functioning of the delicate “instruments of Sensation” (2.7.4), and although men could have no ideas of separate spirits and substances, it was certain that God had. This certainty was all that was required of man: “It is enough to justify the fitness of any thing to be done, by resolving it into the ‘wisdom of God,’ who has done it” (“The Reasonableness of Christianity” Works 6: 134).
- 4 Cf. ECHU 3.6.2: “The measure and boundary of each Sort, or Species, whereby it is constituted that (...)
- 5 Cf. ECHU 3.6.13: “every Substance that exists has its peculiar Constitution, whereon depend those s (...)
8Given that Locke’s Essay was not, in his intention, a manifesto for scepticism, it is worth enquiring whether his pessimism concerning natural science cannot deserve a better name. Locke thought that the scientific knowledge of the species of corporeal bodies was impossible, and the main reason for this claim was that man could never know the real essences of natural species. Since real essences afforded the foundation of the properties of substances,4 their knowledge was required in order to deduce these properties.5 One could still observe and test a substance to determine what properties it might have, but knowledge obtained in this way would never be a complete listing of the properties and could not be known to apply to any other portion of substance, nor be known to hold true of the tested substance in the future.
- 6 Garber 177-78. Locke formulated the corpuscular hypothesis in ECHU 2.8 and used it throughout 2.23. (...)
- 7 Garber 174-75. Given his basic epistemology and his view of sensitive knowledge, Locke could not be (...)
9Daniel Garber affirms that Locke’s “pessimism with regard to our ability to know the real properties that bodies have, their true natures, can be thought of as a kind of scepticism” which he characterizes as “corpuscular scepticism.”6 According to Garber, Locke was concerned more with this kind of scepticism, that is with the problem of discovering the minute insensible corpuscles which constitute the real essence of bodies, than with the problems connected with a representative theory of perception; he was “not particularly worried about how we can know what things are like on the other side of our ideas, as the veil-of-perception sceptic is.” What concerned Locke, in Garber’s view, was something quite different from what Berkeley thought: “If the gross bodies of our everyday experience are really made up of parts too small for us to sense, as the corpuscularians tell us, then how could we ever discover the hidden nature and real constitution of things?”7
- 8 Scientia was for Locke a “certain universal knowledge” (ECHU 4.3.29, 559), whose objects were the r (...)
- 9 A tradition of interpretation going back through Peter Alexander to Maurice Mandelbaum would have L (...)
- 10 Cf. ECHU 2.23.11, 301: “Had we Senses acute enough to discern the minute particles of Bodies, and t (...)
- 11 Cf. ECHU 2.23.11-22 and 32.
10In his Essay Locke affirmed that experimental philosophy had not and would never have the status of a science because of man’s inability to know the nature of physical things with certainty: we shall never “be able to discover general, instructive, unquestionable Truths concerning them. Certainty and Demonstration, are Things we must not, in these Matters, pretend to” (ECHU 4.3.26, 557). Having retained the Aristotelians’ and Cartesians’ notion of scientia as an ideal,8 and having absorbed the import of Boyle’s experimental method as well, Locke was driven to pessimism about the kind and extent of knowledge attainable in natural philosophy: “the meanest, and most obvious Things that come in our way, have dark sides, that the quickest Sight cannot penetrate into” (4.3.22, 553). Nonetheless, if we interpret Locke as identifying a material substance’s real essence with some subset of its constituent corpuscles’ primary qualities, we can accept the point made by Garber and other commentators9 and consider the nature of corpuscular scepticism as surmountable: in Locke’s opinion, the type of ignorance resulting from our inability to perceive minute corpuscles is curable provided that we have “more acute senses or more powerful microscopes,”10 and this implies that he thought that corpuscular scepticism could be overcome, at least in theory.11 In this sense, he could think it possible that our knowledge of physical objects, “under the present Circumstances of our Beings and Constitutions may be carried much farther, than it hitherto has been” (4.3.6, 540).
11This optimistic view presumes that Locke committed himself to the corpuscular hypothesis, which is not beyond doubt. In Some Thoughts concerning Education, for example, Locke affirms that
the Systems of Natural Philosophy, that have obtained in this part of the World, are to be read, more to know the Hypotheses, and to understand the Terms and Ways of Talking of the several Sects, than with hopes to gain thereby a comprehensive, scientifical, and satisfactory Knowledge of the Works of Nature: Only this may be said, that the modern Corpuscularians talk, in most Things, more intelligibly than the Peripateticks. (STCE sec. 193, 247)
- 12 Secondary qualities would be the object of those “Ideas, that our complex ones of Substances are ma (...)
- 13 The simple ideas that form our complex Ideas of substances have a necessary connection or inconsist (...)
12However, in the Essay Locke accepted some components of the corpuscular hypothesis: material bodies are said to be compounded from minute particles and some of their observable qualities to be reducible to the particles’ primary qualities of size, shape and motion. Moreover, Locke seems to identify the real essence of bodies with primary qualities when he affirms that we could discover the internal constitutions of bodies if only we knew the “Texture and Motion of the minute Parts of corporeal things” (ECHU 2.23.12, 303), or when he says that from a better knowledge of the primary qualities of bodies “we might be able to know a great deal more of these Operations of them one upon the other” (4.3.13, 545). Yet Locke seemed to despair of the possibility of understanding how secondary qualities12 are produced by primary qualities and how they were able in their turn to produce sensation; the reductive thesis of corpuscularianism, which was expected to explain how “any size, figure or motion of any Particles, can possibly produce in us the Idea of any Colour, Taste or Sound whatsoever” (4.3.13, 545) was unable to offer any conceivable connection between primary and secondary qualities, not only because of human ignorance of the “size, figure and texture of Parts” primary qualities were made of, but also because of our inability to know with certainty “the Co-existence, or Inco-Existence […] of different Ideas in the same Subject” (4.3. 12).13 Since men are not able “to discover any connexion betwixt these primary qualities of Bodies, and the sensations that are produced in us by them”, they will never be “able to establish certain and undoubted Rules, of the Consequence or Co-Existence of any secondary Qualities” (4.3.13, 545); as a consequence, the only way of understanding how sensations were produced is that of attributing the whole process to God (4.3.6).
13Another phenomenon too obscure for corpuscularianism to illuminate was communication of motion. The corpuscularian notion of impulse, in which bodies interact causally communicating motion to one another by impact, was taken by Locke to be fundamental to our conception of body along with cohesion and extension; nonetheless he considered the nature of the phenomenon to be as mysterious as the one by which the mind moves the body:
in the communication of Motion by impulse, wherein as much Motion is lost to one Body, as is got to the other, which is the ordinariest case, we can have no other conception, but of the passing of Motion out of one Body into another; which, I think, is as obscure and unconceivable, as how our Minds move or stop our Bodies by Thought. (ECHU 2.23.28, 311)
- 14 In dealing with the problem of coherence between naturally indivisible particles, Newton rejected t (...)
14Equally mysterious is the phenomenon of cohesion, which troubled all those who adopted the atomist version of corpuscularianism: the restricted set of properties which atomism traditionally allowed to particles (shape, size and motion) afforded no obvious resources for explaining how they could cohere with one another to form compound bodies.14 An understanding of cohesion was essential to an understanding of the idea of body; if the first was unattainable, the idea of body could not be founded on any genuine understanding of it (ECHU 2.23.24).
15Some years later, another phenomenon, gravitation, was to trouble Locke, leading him to an important shift in opinion. Being at first sympathetic to strict mechanism as the hypothesis supported by the orthodox version of corpuscularianism, Locke held impulse to be the sole means by which bodies could causally interact and, as a consequence, in the first three editions of the Essay, he denied matter the power of acting at a distance (“It is impossible to conceive, that Body should operate on what it does not touch”: 2.8.11, 135). The publication of Newton’s Principia, implying as it did the possibility of action at a distance, led Locke to abandon strict mechanism: in the fourth edition of the Essay he omitted a clause (2.8.12) which denied the possibility of action at a distance, and replaced a statement relating to the way bodies operate one upon another with one relating to the way we could conceive of them operating (2.8.11): “how Bodies produce Ideas in us […] is manifestly by impulse, [this being] the only way which we can conceive Bodies operate in”). The same shift in opinion is manifest in Locke’s second Reply to Stillingfleet:
The gravitation of matter towards matter, by ways inconceivable to me, is not only a demonstration that God can, if he pleases, put into bodies powers and ways of operation, above what can be derived from our idea of body, or can be explained by what we know of matter, but also an unquestionable and every visible instance, that he has done so. (Works 3: 497)
16Locke speaks here of gravitational attraction as a power superadded by God to matter, not as something essential to it: gravity is supposed to have been annexed to matter by a divine action and does not bear any intrinsic connection to the real essence of matter. However, superaddition had already been invoked in the Essay in relation to the difficulties raised about the ability of the corpuscular hypothesis to explain sensation, motion and cohesion:
the coherence and continuity of the parts of Matter; the production of Sensation in us of Colours and Sounds, etc. by impulse and motion; nay, the original Rules and Communication of Motion being such, wherein we can discover no natural connexion with any Ideas we have, we cannot but ascribe them to the arbitrary Will and good Pleasure of the Wise Architect. (ECHU 4.3.29, 560)
17Surely the recourse to superaddition seems to compromise the possibility of overcoming corpuscular scepticism: this is exactly what Margaret Wilson has argued, insisting on Locke’s recognition of the explanatory limitations of the corpuscular hypothesis. In Wilson’s view, Locke was not a consistent Boylean mechanist because he acknowledged that our ignorance about bodies had more profound causes than our ignorance about the primary qualities of their constituent corpuscles; this conviction led necessarily to agnosticism about corpuscularianism, although Locke seemed sometimes to endorse it.
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- 15 Downing 2007: 359.
- 16 Downing takes Locke’s sceptical arguments to show that he did not believe in corpuscularianism: on (...)
18More recently, Nicholas Jolley has reinterpreted strategically those passages of the Essay in which the real essences of material substances appear to be identified with the primary qualities of corpuscles: Locke’s commitment to corpuscularism in these passages is interpreted by Jolley simply as a means to criticize the Aristotelians, while corpuscular scepticism is his way of opposing the Cartesians. In the same vein, Lisa Downing has affirmed that Locke considered the corpuscularians’ distinction between primary and secondary qualities as less fundamental than the metaphysical distinction between real and nominal essence: according to Downing, Locke used the corpuscular hypothesis only as an illustration15 of this last distinction and not as a physical theory capable of standing by itself. Although he considered corpuscularianism to be the theory best suited to our sensory capacities and understanding, in Downing’s view Locke spoke of it only as a hypothesis crippled by explanatory limitations.16
- 17 Works, 2: 413-440. The treatise was composed for young Frank Cudworth, the son of Lady Masham.
- 18 Elements 440: “these sensible bodies are made of [...] unconceivably small bodies, or atoms, out of (...)
19This sceptical reading of Locke’s corpuscularianism seems to be contradicted by a little treatise he composed sometime after 1698, entitled The Elements of Natural Philosophy.17 Here Locke embraced the atomist version of the corpuscular hypothesis emphasizing its explanatory power,18 and summed up the principal elements of the Newtonian synthesis of the physical and astronomical universe, reaffirming the possibility of action at a distance: “Two bodies at a distance will put one another into motion by the force of attraction; which is inexplicable by us, though made evident to us by experience, and so to be taken as a principle in natural philosophy” (Elements 417).
- 19 Few commentators interpret Newton’s idea of action at a distance as grounded in a superadded proper (...)
20Locke’s agreement with Newton in The Elements, the only work on natural philosophy ever attempted by him, seems complete; both show a strong sympathy for atomism and consider the power of gravitational attraction as inessential to matter, though Newton probably did not ground it on superaddition.19 This agreement was already manifest in Some Thoughts Concerning Education, where Locke spoke enthusiastically of Newton’s “admirable book”:
Though the Systems of Physicks, that I have met with, afford little encouragement to look for Certainty or Science in any Treatise which shall pretend to give us a body of Natural Philosophy from the first Principles of Bodies in general, yet the incomparable Mr. Newton has shewn, how far Mathematicks applied to some Parts of Nature may, upon Principles that Matter of Fact justifie, carry us in the knowledge of some, as I may so call them, particular Provinces of the Incomprehensible Universe. And if others could give us so good and clear an account of other parts of Nature, as he has of this our Planetary World, and the most considerable Phænomena observable in it, in his admirable book, Philosophiæ naturalis principia Mathematica, we might in time hope to be furnished with more true and certain Knowledge in several Parts of this stupendous Machin [sic]. (STCE sec.194, 248)
21Some time later, in his Conduct of the Understanding, Locke again celebrates Newton’s Principia, insisting on the opportunity to investigate the most fundamental truths and mentioning the law of universal gravitation as one of them (sec. XV). Nonetheless, complete agreement with Principia seems insufficient to overcome Locke’s corpuscular scepticism. As Margaret Wilson has pointed out, Locke could not be convinced that the mechanico-corpuscular view was the ultimate truth on matter, since he considered possible within the realm of nature that matter be endowed with the power of thinking. Had Locke been a consistent mechanist, argued Wilson, he should find impossible to ascribe thinking to matter: a strict dualism of substances was requisite to accommodate for a strict, Boylean mechanical conception of matter; nonetheless in the Essay Locke contemplated the possibility of thinking-matter, invoking superaddition once again.
- 20 See Works, 3: 33, 37.
- 21 Just one example from the Second Reply, 469: “I know nobody, before Des Cartes, that ever pretended (...)
22It is true that, at the level of probability and belief, in the Essay Locke rather favours the immateriality of human soul. Moreover, in his Letter to Stillingfleet, he affirms repeatedly that “it is in the highest degree probable that the thinking substance in us is immaterial.”20 Nonetheless in the same set of letters he gives a fully-fledged defence of the thinking-matter conjecture, with a host of new arguments in its favour.21
- 22 In a later manuscript note entitled “Spirit, Soul and Body”, written probably in preparation to A P (...)
23Actually Locke thought the thinking-matter conjecture worth investigation, as some published and unpublished materials reveal,22 and in the Essay (4.3.6, 540) he allowed the possibility of “some Systems of Matter fitly disposed” to be endowed with the power of thinking, though he vindicated pure agnosticism on this topic. Of course, thinking matter was a possible solution to the problem of intelligibly relating mental and physical states, yet it is dubious whether it could suffice in Locke’s opinion to eliminate the most “incurable” kind of ignorance he had pointed in the Essay (4.3.12), the true source of his pessimism about scientific knowledge:
we neither know the real Constitution of the minute Parts [of any Substance], on which their Qualities do depend; nor, did we know them, could we discover any necessary connexion between them, and any of the secondary Qualities: which is necessary to be done, before we can certainly know their necessary co-existence. (ECHU 4.3.14, 546)
24The necessity of this connection is what really troubled Locke, given the limits he acknowledged to our cognitive faculties. Nonetheless, he had some hopes in the future perfectibility of the corpuscular hypothesis, as I will try to illustrate briefly. In order to value the true import of Locke’s attitude towards corpuscularianism, it is useful to remember that he called it the hypothesis “which is thought to go farthest in an intelligible Explication of the Qualities of Bodies” (ECHU 4.3.16, 547). Of course, we might doubt that Locke himself thought that corpuscularianism could go farthest in intelligibly explaining the qualities of bodies: the cohesion of matter and the communication of motion, two foundations of the corpuscularian world, could not be explained by the resources afforded by the theory. Nonetheless, Locke believed that corpuscularianism was uniquely intelligible and rejected any inference from inconceivability to impossibility. In the Essay, Locke acknowledged that thinking-matter was inconceivable, but claimed that the alternative of mind-body interaction was equally inconceivable, and protested against
an unfair way which some Men take with themselves: who, because of the inconceivableness of something they find in one, throw themselves violently into the contrary Hypothesis, though altogether as unintelligible to an unbiased Understanding. (ECHU 4.3.6).
25In Locke’s view, there are situations in which both a hypothesis and its contrary are inconceivable, and this means that he must believe that some truths are inconceivable: he believes that cohesion and impulse are both real and impossible to explain. Locke’s belief in the reality of the inconceivable is attested by his second Reply to Stillingfleet, where he abandons his original conclusion that all corporeal interactions occur through impulse:
It is true, I say “that bodies operate by impulse and nothing else.” And so I thought when I writ it, and can yet conceive no other way of their operation. But I am since convinced by the judicious Mr. Newton’s incomparable book, that it is too bold a presumption to limit God’s power, in this point, by my narrow conceptions. The gravitation of matter towards matter, by ways inconceivable to me, is not only a demonstration that God can, if he pleases, put into bodies powers and ways of operation, above what can be derived from our idea of body, or can be explained by what we know of matter, but also an unquestionable and every where visible instance, that he has done so. (Works 3: 467 f.)
26According to Locke, the conceivability of a hypothesis and the inconceivability of alternatives provide us with good grounds to believe the conceivable hypothesis; surely these grounds are not utterly conclusive, so that conceivability is not an infallible guide to truth. Nonetheless, given his emphasis on our cognitive limits, Locke seems to believe that a true theory might be inconceivable: after calling corpuscularianism a hypothesis, he remarks that he fears that
the Weakness of humane Understanding is scarce able to substitute another, which will afford us a fuller and clearer discovery of the necessary Connexion and Co-existence of the Powers, which are to be observed united in several sorts of [bodies]. (ECHU 4.3.16).
27In Locke’s opinion, if corpuscularianism is false we will not find a better theory with different, conceivable forms of interaction and we will not be able to understand how the world works; of course, this does not suffice to make corpuscularianism true, but it is enough to let us accept it, remembering that “a little knowledge is still knowledge and not scepticism.”