 In addition to the kinds of ideas noted above, there are also particular and abstract ideas. Particular ideas have in them the ideas of particular places and times which limit the application of the idea to a single individual, while abstract general ideas leave out the ideas of particular times and places in order to allow the idea to apply to other similar qualities or things. There has been considerable philosophical and scholarly debate about the nature of the process of abstraction and Locke’s account of it. Berkeley argued that the process as Locke conceives it is incoherent. In part this is because Berkeley is an imagist—that is he believes that all ideas are images. If one is an imagist it becomes impossible to imagine what idea could include both the ideas of a right and equilateral triangle. Michael Ayers has recently argued that Locke too was an imagist. This would make Berkeley’s criticism of Locke very much to the point. Ayers’ claim, however, has been disputed (see, for example, Soles 1999). The process of abstraction is of considerable importance to human knowledge. Locke thinks most words we use are general (III.1.1, N: 409). Clearly, it is only general or sortal ideas that can serve in a classificatory scheme.