Is Locke’s distinction between primary and secondary qualities clear and consistent?

Submitted for PH201 (History of Modern Philosophy) Summer Exam

This essay presents Locke’s separability and resemblance criteria for distinguishing between primary and secondary qualities, and argues that the distinction can survive under scrutiny, if it is understood through the lens of his corpuscularian commitments.

One might see Locke’s distinction as a response to Descartes’ example of how, when a piece of wax is melted, all of its sensory qualities (its taste, smell, colour, shape, sound, temperature, hardness) disappear, and nevertheless one judges that the same piece of wax remains. This is a challenge to the empiricist assumption that knowledge is acquired solely through the senses; the mind must have an innate intellectual capacity to grasp the idea of a substance that is merely extended, flexible, and changeable, in spite of how its sensory features change.

Thus, a primary quality of an object is one which is ‘utterly inseparable’ from it. That is to say, however the object is altered or transformed, that quality – examples of which include “Solidity, Extension, Figure, Motion, or Rest, and Number” – remains. In contrast, secondary qualities like “Colours, Sounds, Tastes”, are not in this way separable; they are “nothing in the Objects themselves, but Powers to produce various Sensations in us”, a power which emerge from the combination of primary qualities acting together. This definition leads to a second way of distinguishing the two kinds of qualities: ideas of primary qualities resemble the corresponding feature of the object itself, while secondary, or “imputed” qualities, as mere powers, do not.

Several criticisms are immediately apparent. In the first place, one might ask whether, in the separability criterion, Locke is referring to determinables (like colour) or determinates (like red, blue, or yellow). It cannot be his argument that determinate primary qualities are inseparable from objects, since clearly the particular determinates of the primary qualities he give can change when an object is transformed; we can clearly change an object’s figure, for instance. So he must mean that primary determinable qualities are inseparable from objects. But one might argue that secondary determinable qualities are likewise inseparable; one can change an object’s colour, but not remove its colour entirely. Moreover, the resemblance criterion appears incompatible with Locke’s representative realism, according to which we only experience the external world indirectly through ideas objects engender in us. Thus it seems senseless to suppose that sensory input can shed any light on whether an idea resembles the underlying physical object, when by definition, we never have unmediated access to the object.

Against the first criticism, Locke can respond that secondary determinable qualities depend on perceivers; that is to say, an object only has a colour when it is being perceived. On the other hand, primary qualities exist in objects even without direct sensory observation. This is the sense in which they are “inseparable” from objects. A tree in a forest, absent any observer, must still have solidity, extension, figure, and so on – it is inconceivable to think it is shapeless in such a scenario (“ a body with no extension or shape” collapses into incoherence – we would no longer be thinking of a body). But it is perfectly intelligible to suppose that if it falls, it doesn’t make a sound, since that is simply a power it produces in observers. Its primary qualities still interact in the same way to produce sound waves, but with no observer, it has no sound (hence, sound is a secondary quality). Hence, Locke is often thought to be arguing that primary qualities are “intrinsic”, while secondary qualities are found only the interaction of the object with the world. We can understand both this view, and Locke’s response to the second criticism about resemblance, by understanding his micro-structural story. The distinction between primary and secondary qualities is motivated by his commitment to corpuscularianism, the view that any physical object is composed of tiny particles (‘corpuscles’) whose basic qualities – such as motion, size, and shape -- determine the properties of the object. Even when no colour is present, the corpuscular “primary” arrangement (size, figure, motion of particles) remains. These micro-features ground the dispositional power to produce colours or sounds, but the power does not amount to a colour actually being in the object until the relational conditions are met. And it is in this sense that primary qualities “resemble” the bodies themselves, and are intrinsic.

This response to these criticisms shows that his distinction is certainly consistent, in the sense that it is well-defined and does not collapse immediately into incoherence. That is, the ostensible tension between the other views he advocates in his Essay Concerning Human Understanding and the separability and resemblance criteria disappears when one considers the corpuscularian dimension. Furthermore, this account corroborates Locke’s view that the resemblance of primary qualities and objects explains how physical objects engender ideas of each kind of quality in us.

Nevertheless, there are other criticisms that have been raised, most notably by Berkeley. One objection he raises is that since by “resemblance”, one means that both relata share properties, it is absurd to suggest that an idea can resemble an object at all: he says “an idea can be like nothing but an idea”; it cannot have extension or figure in the way Locke claims objects do. Jacovides has argued that “the best reading of Locke’s theses takes them literally”, suggesting that Berkeley’s literal reading has force; it was a “common doctrine” in Locke’s time that objects and ideas might be related in this way. As well as this, Berkeley argued that primary qualities cannot be inseparable or intrinsic to objects, since one and the same grain of rice can appear to be large to a mite, yet small to a human. Hence, Locke’s view leads to a paradox of conflicting appearances: it cannot be the case that the same glass of water leads to the idea of hot in one person, and cold in the other, and for both incompatible ideas to be veridical.

Despite Jacovides suggestion that Locke may have meant what Berkeley takes him to mean, it is overly ungenerous to suppose that Locke argued that ideas and objects were the same kind of thing, and that their “resemblance” is to be understood in terms of ideas possessing primary qualities, rather than being of those qualities. Such a view is plainly unworkable, and the textual evidence – setting aside the historical intellectual context – is slim. Granted, Locke writes “the Power to produce any Idea in our mind, I call Quality of the subject”; but if we interpret this in the sense argued for previously, there is no real difficulty here. Moreover, the problem of conflicting appearances is similarly unproblematic. If we understand this, as Kalderon advocates, as a paradox in which an object cannot have two incompatible qualities if both qualities are veridical, Locke need only deny that one of variation, incompatibility, and veridicality holds in any given case. In the example of the mite, it is straightforward to deny that the small and large appearances are incompatible, since size is a relational quality: the grain of rice can be small-to-me and large-to-the-mite with no contradiction. It is easy to argue similarly in response to any particular apparent contradiction Berkeley might raise.

Hence, Locke’s distinction between primary and secondary qualities, though it appears contradictory, can be clarified through the doctrine of corpuscularianism, in such a way that both the separability and resemblance criteria are clear and consistent. Moreover, I have shown that Berkeley’s criticisms either misunderstand Locke’s distinction, or fail to disturb it.

Result

Mark: 74% (Low First), averaged across this and two other answers.