Abstract

It is an old charge against Locke that his commitment to a common substratum for the observable qualities of particular objects and his empiricist theory about the origin of ideas are inconsistent with one another. How could we have an idea of something in which observable qualities inhere if all our ideas are constructed from ideas of observable qualities? In this paper, I propose an interpretation of the crucial passages in Locke, according to which the idea of substratum is formed through an elaborate mental process which he calls “supposition.” It is the same process we use when we form the idea of infinity − another problematic idea for an empiricist. In the end, Locke was more liberal than most empiricists in subscribing to the existence of ideas far removed from experience, because he accepted supposition as a legitimate way of constructing new ideas.