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Journal of the History of Philosophy 40.2 (2002) 201-228

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Locke's Primary Qualities

Robert A. Wilson


1. Introduction

in chapter viii of book ii of An Essay Concerning Human Understanding, 1 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. 2

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. 3 A central motivation for this paper is the idea that these two tasks are crucial, mutually constraining components in understanding Locke's view of primary qualities. [End Page 201]

The most radical and interesting exception to the general trend of operating with a more or less composite list of primary qualities is Peter Alexander's interpretation of Locke in chapter 6 of his Ideas, Qualities and Corpuscles. 4 Alexander holds that for Locke there are only three primary qualities: size, shape, and mobility. Some of the properties that feature in Locke's lists (bulk, extension, figure, and motion/rest) simply refer to these properties. Others (solidity, texture, situation, number, and motion of parts) are not primary qualities at all. Alexander's view of what is and is not a Lockean primary quality is governed by an overarching corpuscularian interpretation of Locke, and by Alexander's view of the nature of Locke's debt to Boyle in particular. According to Alexander, primary qualities are qualities that the most fundamental things--single corpuscles--have in and of themselves, and that are to be invoked in providing non-occult explanations for the observable properties possessed by observable bodies. Given this understanding of corpuscularianism and of the notion of a primary quality, texture and number and motion of parts are not primary qualities because they are not properties that single corpuscles can have, being instead properties of clusters of corpuscles; likewise, situation is not a primary quality, since although it is a property of single corpuscles, it is a relational property, and so not a property they have in and of themselves. 5

While Alexander's assumption that there is more systematicity in Locke's putative lists of primary qualities than others have found is surely correct, his claim that, for Locke, there are only three primary qualities requires the problematic move of dismissing or reinterpreting many of these lists. I shall argue that there are strong grounds to hold that both solidity and texture are primary qualities for Locke and, in fact, that all of the qualities named in Locke's putative lists of primary qualities in II.viii are primary qualities for Locke. While my interpretation generates a list of primary qualities similar to that given by simple composition, developing it will reveal both nuances of Locke's discussion in II.viii and the sophistication of his view of primary qualities, neither of which has been fully appreciated.

The general corpuscularian background to Locke's views, and why Locke's discussion of primary and secondary qualities should be viewed against this background, have been amply discussed by others. 6 Less has been said, however, about the reason and order to Locke's various lists of primary qualities in II.viii. After offering my own interpretation of the nature of Locke's primary qualities (section 2...