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. (shrink)