Online research in philosophy

Introduction in chapter viii of book ii of An Essay Concerning Human Understanding, John Locke provides various putative lists of primary qualities. Insofar as they have considered the variation across Locke's lists at all, commentators have usually been content simply either to consider a self-consciously abbreviated list (e.g., "Size, Shape, etc.") or a composite list as the list of Lockean primary qualities, truncating such a composite list only by omitting supposedly co-referential terms. Doing the latter with minimal judgment about what terms are co-referential gives us the following list of eleven qualities (in the order in which they appear in this chapter of the Essay): solidity, extension, figure, mobility, motion or rest, number, bulk, texture, motion, size, and situation. Perhaps surprisingly given the attention to the primary/secondary distinction since Locke, Locke's primary qualities themselves have received little more than passing mention in the bulk of the subsequent literature. In particular, no discussion both offers an interpretation of Locke's conception of primary qualities and makes sense of Locke's various lists as lists of primary qualities. A central motivation for this paper is the idea that these two tasks are not independent.

That corpuscularianism played a critical role in Locke’s philosophical thought has perhaps now attained the status of a truism. In particular, it is universally acknowledged that the primary/secondary quality distinction and the conception of real essence found in the Essay Concerning Human Understanding cannot be understood apart from the corpuscularian science of Locke’s time.1 When Locke provides lists of the primary qualities of bodies,2 the qualities that “are really in them whether we perceive them or no,” those lists show strong resemblances to Robert Boyle’s views about the “primary affections” of matter, as expressed in such influential programmatic works as On the Origin of Forms and Qualities.3 Moreover, Locke’s conception of the real essences of bodies, the inner constitutions which serve as the causal sources of all their properties, typically appears to be a corpuscularian one.4 Nevertheless, the question of the nature of Locke’s philosophical allegiance to corpuscularianism remains a controversial one.5..

Locke denied that ideas of secondary qualities resemble their causes. It has been suggested that Locke denied this because he accepted a mechanical corpuscular hypothesis about the constitution of objects. This paper shows that this and other usual explanations of Locke's denial are mistaken. Further, it suggests an alternative relationship between the scientific account and Locke's philosophical views, and finally it provides Locke's real justification for his claim that ideas of secondary qualities do not resemble their causes.

QUESTIONS Objects seem to have some properties in themselves (like shape), and some other properties that depend on other things around them (like being alone or accompanied). The distinction between primary and secondary qualities is a special case of this more general contrast: what, according to Locke, is the basis for the distinction? Is there more than one way to understand Locke’s argument: what is the best reading of Locke? What wider significance does the distinction between primary and secondary qualities have?

Locke’s argument for the primary-secondary quality distinction is compared with Descartes’s argument (in the Principles of Philosophy) for the distinction between mechanical modifications and sensible qualities. I argue that following Descartes, Locke’s argument for the primary-secondary quality distinction is an essentially a priori argument, based on our conception of substance, and the constraints on intelligible bodily interaction that this conception of substance sets.

John Locke’s distinction between primary and secondary qualities of objects has meet resistance. In this paper I bypass the traditional critiques of the distinction and instead concentrate on two specific counterexamples to the distinction: Killer yellow and the puzzle of multiple dispositions. One can accommodate these puzzles, I argue, by adopting Thomas Reid’s version of the primary/secondary quality distinction, where the distinction is founded upon conceptual grounds. The primary/secondary quality distinction is epistemic rather than metaphysical. A consequence of Reid’s primary/ secondary quality distinction is that one must deny the original version of Molyneux’s question, while one must affirm an amended version of it. I show that these two answers to Molyneux’s question are not at odds with current empirical research.

Reid offers an under-appreciated account of the primary/secondary quality distinction. He gives sound reasons for rejecting the views of Locke, Boyle, Galileo and others, and presents a better alternative, according to which the distinction is epistemic rather than metaphysical. Primary qualities, for Reid, are qualities whose intrinsic natures can be known through sensation. Secondary qualities, on the other hand, are unknown causes of sensations. Some may object that Reid's view is internally inconsistent, or unacceptably relativistic. However, a deeper understanding shows that it is consistent, and relative only to normal humans. To acquire this deeper understanding, one must also explore the nature of dispositions, Reid's rejection of the theory of ideas, his distinction between sensation and perception, and his distinction between natural and acquired perceptions.

The first half of this review article on Locke on primary and secondary qualities leads up to a fairly straightforward reading of what Locke says about the distinction in Essay II.viii, one that, in its general outlines, represents a sympathetic understanding of Locke’s discussion. The second half of the paper turns to consider a few of the ways in which interpreting Locke on primary and secondary qualities has proven more complicated. Here we take up what is sometimes called the Berkeleyan interpretation of Locke (section 6), the understanding of Locke’s resemblance thesis (section 7), and Locke’s views of qualities and their relationship to powers (section 8).