  Berkeley’s point is thus well taken. It is worth noting that, in addition to undermining the materialist’s attempted inference to the best explanation, Berkeley’s point also challenges any attempt to explain representation and mediate perception in terms of causation. That is, the materialist might try to claim that ideas represent material objects, not by resemblance, but in virtue of being caused by the objects. (Though neither Descartes nor Locke spells out such an account, there are grounds in each for attributing such an account to them. For Descartes see Wilson 1999, 73–76; for Locke see Chappell 1994, 53.)  However, PHK 19 implies that the materialists are not in a position to render this account of representation philosophically satisfactory.