Locke's "support" for corpuscularian mechanism

The philosophy of body was one of the most controversial issues in the seventeenth-century. It defined who was and was not party to the scientific revolution of the “new sciences.”

In Locke’s context, there are five competing theories about matter. First, there is the Scholastic-Aristotelian doctrine of four elements (earth, fire, air, and water), part of a larger metaphysical theory of substance. The causal agents in real alterations in body are substantial forms and real qualities. The mode of causality is non-mechanistic and teleological. Second, there is the spagyritic chemistry or iatrochemistry. This movement is an extension of the alchemical tradition developed by Paracelsus and his followers, the van Helmonts, according to which there are three principles or basic causal agents of matter: salt, sulfur, and mercury. Mercury is an active or vital (supra-material) principle. Third, there are the Cambridge Platonists who argue that there are immaterial causal agents which actively determine all changes in matter. Fourth, there is the Cartesian natural philosophy, based on the identification of matter with extension. Finally, there is the corpuscularian philosophy or mechanistic atomism.

The Cartesian natural philosophy and corpuscularian mechanism are considered mechanistic, but they differ greatly. The Cartesians hold that a void is not possible, since they identify matter with extension, conceive of matter as infinitely divisible, and deny the existence of atoms. Corpuscularians hold that solidity is also part of the essence of matter, allowing for voids and affirming the existence of atoms.

The core theses of corpuscularianism are as follows. (1) All matter is the same in kind—viz., solid extended substance. (2) All bodies are either (a) individual corpuscles which are physically indivisible and which have as their only qualities (in addition to extension and solidity) size, shape, location, motion or rest, and number or (b) collections of corpuscles. There are no physically real components or constituents of a body beyond its component corpuscles. Compound bodies have a further quality—“texture,” which is the arrangement of the component corpuscles resulting from their various sizes, shapes, relative situations, and relative motions. (3) Alterations in bodies are due to a change in texture; all changes in texture are the result of impact or contact action of one body upon another. In short, all causation involving bodies is mechanical causation.

This way of conceiving of body owes to the atomism of Democritus, Epicurus, and Lucretius. Gassendi revives this in France in the seventeenth-century. It is affirmed in England by Thomas Hobbes, Walter Charleton, and Robert Boyle, who has a tremendous influence on Locke.

In the “Epistle” and indeed in many places of the Essay, Locke appears to approve of corpuscularian mechanism. Interpreting Locke’s “approval” is tricky business. There is a tradition of interpretation going back through Peter Alexander and J. L. Mackie to Maurice Mandelbaum which would have Locke completely affirm corpuscularianism as “the” truth about the very nature of body. That tradition does two things: (a) it alleges that Locke’s actual use of the corpuscularian hypotheses is evidence that he wholly subscribes to that theory of body as “the” truth about body, and (b) it alleges that Locke actually uses corpuscularian hypotheses in his reasoning to analyze the representative character of perceptions.

While it is true that Locke says he is aiming to clear away some of the rubbish which stands in the way of knowledge, and while it is also true that he fights against the Cartesians and Scholastic-Aristotelians, it is equally true that he does so within an ambit of such a pervasive skepticism about the powers of human cognition that he would not endorse as “the” truth any theory of the nature of body, including corpuscularian atomism. Given the severe restrictions he places on the informational content in perceptual representation from his theory of perceptual representation (i.e., perceivers at best have sensitive knowledge that bodies exist and have “powers”), how could Locke either claim to have knowledge of the nature of body or use premises about body (e.g., corpuscularian mechanisms in perception) as more than merely helpful aids in discoursing about the scope of ideas?

Can Locke fight against the aforementioned foes and still remain qualifiedly noncommittal about what he advances as superior to them? He can and does. It turns on properly interpreting Locke’s theory of perceptual representation, in which a very attenuated conception of “theory” is held fixed. Locke works with some initially crude reflections on the mundane deliverances of the senses concerning bodies. He reflects on what he finds himself believing on an everyday, commonsense level: if one splits a loaf of bread in half, the result will be two smaller loaves of bread, and so on; if one bumps a billiard ball with another, then the second ball usually moves or alters as a result, and that seems to be how changes are wrought in bodies generally; if one reflects on the way everyone uses the term “body,” then one cannot help but think of some solid, extended substance; etc.

Again, the attitude is experimental and commonsense as opposed to dogmatic or obscurantist, the latter two vices being exemplified by Cartesianism and Scholastic-Aristotelianism. Because of his experimental attitude, the relation between the deliverances of commonsense and the truth is indirect at best. As it happens, Boylean corpuscularianism fits really well with commonsense considerations about the nature of body. In short, the corpuscularian hypothesis is thinkable and sensible, whereas Cartesianism and Scholastic-Aristotelianism are too remote from sense and sensibility to be thought of clearly and distinctly. For that minimal reason, corpuscularianism is to be preferred, since at least it is something that Locke can make sense of in his reflections.

Does this mean that it is “closer to the truth of the nature of body?” By Locke’s lights, it probably does not mean any such thing. At the very best, it may imply some truth-conducivity owing to some bare article of epistemic faith, indeed the same one possibly operative in his musings on perceptual representation: maybe, if one sticks to what one can think about sensibly, one might arrive at categories that are closer than not to the truth. Even this article of faith may be too optimistic for Locke to endorse. His attitude is one of modesty and hope especially in light of such a dim candle that so many abuse for sake of a chimerical goal regarding the nature of body: scientia.

Thus Locke can use corpuscularianism as a helpful way of talking about bodies under conceptions that are readily understood. He can oppose the Cartesians and Scholastic-Aristotelians for the simple reason that neither he nor anyone else who reflects seriously on their theories can understand what they are actually saying. For all he knows, however, they could be right about the nature of body. Not only could the Scholastic-Aristotelians be right about body, corpuscularianism might be dreadfully wrong. There may be something even more fundamental in bodies that is outside of the scope of human conceivability, as Locke concedes in IV.iii.11. In the case either of Scholastic-Aristotelianism or the more remote mechanics of body, humans would be in a position neither to know what body is really like nor to dialog concerning ideas vis-à-vis bodies at all. With corpuscularianism, at the very least perceivers, given their cognitive endowments, can talk about ideas vis-à-vis bodies, even if they can never have scientia concerning the relation. Since if one is going to have opinions about anything, one ought only opine what one can conceive, it is better to opine the tenets of corpuscularianism than anything else. Granted, corpuscularianism could be wildly wrong about the nature of body, but it is the best bet given the profoundly limited powers of the human understanding. If corpuscularianism turns out to be dreadfully wrong, at least one is wrong in the least epistemically blameworthy way.

This modest, crypto-Pyrrhonian strategy is all that Locke has in mind when he claims to clear aside rubbish which stands in the way of knowledge. If one takes Locke to be building a foundation for English corpuscularianism, then this modest foundation is all that the human understanding can construct. Thin as it is, however, it is still to be preferred to either nothing at all or the dogmatic/obscurantist theories of matter competing against corpuscularianism.