2. Locke's Substratum Theory

Locke has a theory about the idea of substance considered as a ‘substratum’ or ‘support’ of qualities.1 It is a strange theory, according to which one part of our conceptual apparatus is both important and disreputable. Nothing else in the writings of any philosopher matches the doubleness of attitude of the passages about substratum in Locke’s Essay. This duplicity has been noted by students of Locke, but not explained. I once suggested that Locke believed the hostile side of the theory and intended the favorable side sarcastically, but now I can do better. My new answer—like my old wrong one—presupposes what I shall call the ‘Leibnizian interpretation’ of the substratum texts. This view about what the substratum theory is, though accepted by most Locke students from Leibniz onwards, has lately been attacked. I shall defend it against the most vigorous of those attacks, the one by M. R. Ayers.