METAPHYSICS an idea, not a thought about a tree In thinking it, I am not thinking that the tree is a pretty hazy one Ideas, if you must speak of ideas in this way, are the things we think with; they are not, in general, the things that we think about The opening passage quoted from the Principles already assumes the idealism that is supposed to be the conclusion of a long argument Idealism is implicit in the initial confusion between mental acts and their objects It cannot be said that Berkeley was unaware that this criticism could be levelled Hylas, near the end of the Wrst Dialogue, makes a distinction between object and sensation He says: The sensation I take to be an act of the mind perceiving; besides which, there is something perceived; and this I call the object For example, there is red and yellow on that tulip But then the act of perceiving those colours is in me only, and not in the tulip (BPW, 158) Philonous’ rejection of this takes a very oblique route He picks on the word ‘act’ and proceeds to argue that a sensation—e.g smelling the tulip—is something passive, not active Dubious though that claim is, there is no need for Hylas to controvert it in order to defend his distinction All he has to is to substitute the expression ‘event in the mind’ for ‘act of the mind’ But Philonous sails on to his conclusion by substituting the ambiguous word ‘perception’ for the ambiguous word ‘idea’, and taking it casually for granted that the object of a perception is a part of the perception (BPW, 159) If there is nothing that we can know except ideas, and if ideas can exist only in a mind, then it is not diYcult for Berkeley to reach his conclusion that everything that we can know to exist is in the mind of God: When I deny sensible things an existence out of the mind, I not mean my mind in particular but all minds Now it is plain they have an existence exterior to my mind; since I Wnd them by experience to be independent of it There is therefore some other Mind wherein they exist, during the intervals between the times of my perceiving them: as likewise they did before my birth, and would after my supposed annihilation And as the same is true with regard to all other Wnite created spirits, it necessarily follows that there is an omnipresent eternal Mind, which knows and comprehends all things.5 Berkeley’s proof of the existence of God is considered in detail in Ch 10 202