Abstract ideas also depend on experience. Consider first the abstract idea of white. We form the idea of white by observing several white things: we see that milk, chalk, and snow all have the same sensible quality and call that “white” (2.11.9). We form the idea of white by separating the ideas specific to milk (for example, being a liquid, having a certain flavor), or specific to snow (for example, being cold and fluffy), and attending only to what is the same: namely, being white. We can do the same process of abstraction for complex ideas.
