Coffey: Primary and Secondary Qualities #4

Philosophers have characterized the difference between primary and secondary qualities in various ways.

1. On 9/22 I quoted Coffey's distinction between qualities in actu (perceived) and in potentia  (unperceived) respecting the secondary qualities sweetness, whiteness, etc. He doesn't make and says there is no ground for the same distinction between primary qualities, e.g. roundness, size, etc. (Vol. 2, p. 128-9). Maybe that is because he couldn't conceive of any sort of dissimilarity between such primary qualities perceived and unperceived, and his saying so would have been an indirect agreement with John Locke. Locke: "From whence I think it is easy to draw this observation, that the ideas of primary qualities are resemblances of them, and their  patterns do really exist in the bodies themselves; but the ideas produced in us by these secondary qualities have no resemblance of them" (ECHU, II, VIII, 15). An example of the latter is perceived color versus light wave frequency.

2. Another way of stating the difference is that primary qualities are categorical but secondary qualities are dispositional.  In this context "dispositional" means a quality that is manifested given the appropriate circumstances. Analogous examples: (a) glass is fragile in that it will break if struck hard enough, and (b) sugar or salt is soluble in that it dissolves in water.

3. Another way of stating the difference is primary qualities are intrinsic but secondary qualities are extrinsic or relational.