 A quite different explanatory role is assigned to attention in Bishop Berkeley’s Principles of Human Knowledge, although here again we find that it is in order to remove an epistemological glitch that the notion of attention is brought in. In the Introduction to Principles of Human Knowledge Berkeley rejects Locke’s claim that there exist such things as Abstract Ideas. But Berkeley retains Locke’s commitment to the core empiricist claim that the thinking of thoughts is always a matter of handling ideas received from experience. This would seem to lead to the conclusion that it is not possible to think about abstractia, but Berkeley realizes that that conclusion is unacceptable. It is, as he says, perfectly possible to think about the properties of triangles in general.