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, the understanding of Locke’s resemblance thesis, and Locke’s views of qualities and their relationship to powers. (shrink)

Seth Pringle-Pattison (233n1) observed that Locke “teaches a twofold mystery—in the first place, of the essence (‘for the powers or qualities that are observable by us are not the real essence of that substance, but depend upon it or flow from it’), and in the second place, of the substance itself (‘Besides, a man has no idea of substance in general, nor knows what substance is in itself.’ Bk. II.31.13).” In this paper, I’ll explain the relation between the two mysteries. (...) Our Rosetta Stone is Locke’s argument that we understand body and spirit equally well since we are ignorant of their underlying substances but we “have distinct clear Ideas of two primary Qualities, or Properties” (2.23.30) of each. I’ll show that he is working with a restricted notion of primary quality in this passage, but one that demonstrably falls under the kind defined in his chapter on primary and secondary qualities. According to Locke, the fundamental primary qualities of bodies flow from corporeal substances and the determinations of these fundamental qualities constitute real essences. Locke’s discussion can’t be understood without understanding the relevant scholastic background. In the first half of my paper, I’ll explain his argument as an idiosyncratic application of doctrines he learned and taught at Oxford. In the second half, I’ll use lessons from my interpretation of the argument to explain the relation that Locke believes obtains between a substance and its fundamental primary qualities, and then I’ll build upon that explanation to elucidate his general account (insofar as he has a general account) of the inherence of qualities in corporeal substances. (shrink)

(2009). The Role of Natural Philosophy in the Development of Locke's Empiricism. British Journal for the History of Philosophy: Vol. 17, No. 1, pp. 55-83.

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.