Reid’s Foundation for the Primary/Secondary Quality Distinction

Thomas Reid (1710-1796) 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 distinction betwixt primary and secondary qualities hath had several revolutions. Democritus and Epicurus, and their followers, maintained it. Aristotle and the Peripatetics abolished it. Des Cartes, Malebranche, and Locke, revived it, and were thought to have put it in a very clear light. But Bishop Berkeley again discarded this distinction, by such proofs as must be convincing to those that hold the received doctrine of ideas. Yet, after all, there appears to be a real foundation for it in the principles of our nature.1 And so Reid summarizes the history of thought on sensible qualities, inviting the following questions. Where did these earlier accounts go wrong? What, according to Reid, is the real foundation of the primary/secondary quality distinction? How is it to be found in the “principles of our nature”? Does Reid offer a viable alternative to the views of Locke and others? These are the questions I aim to answer in this paper. Traditionally, the distinction is roughly that primary qualities such as shape, size and motion are in some sense observer-independent features of the world, digitalcommons.unl.edu 1. Thomas Reid, An Inquiry into the Human Mind on the Principles of Common Sense (hereafter Inq), ed. Derek R. Brookes (Edinburgh UP, 1997), V iv, p. 62. R e i d ’ s F o u n d a t i o n F o R t h e P R i m a R y /s e c o n d a R y Q u a l i t y d i s t i n c t i o n 479 while secondary qualities, such as color, smell, taste and sound are more closely tied to our particular (human) perceptual perspective. Beyond this rough characterization, there is little consensus. Many have noted that primary and secondary qualities somehow “involve” dispositions.2 I think that disagreement about the nature of primary and secondary qualities is in large part a disagreement about the nature of this involvement. Consequently some understanding of the nature of dispositions is important to understanding the debate. In §I, I sketch a few accounts of dispositions to serve as a framework for subsequent discussion. In §II, I explore competing accounts of primary and secondary qualities. In §III, I explain why Reid rejects the Lockean accounts. In §IV, I present Reid’s alternative, according to which the distinction is epistemic rather than metaphysical. In §V, I defend the coherence of Reid’s view. In §§VI-VII, I defend Reid against the charge that his distinction collapses upon scrutiny. This defense further explicates the nature of Reid’s distinction.