It is largely the very peculiar kind of being that belongs to universals which has led many people to suppose that they are really mental. We can think of a universal, and our thinking then exists in a perfectly ordinary sense, like any other mental act. Suppose, for example, that we are thinking of whiteness. Then in one sense it may be said that whiteness is “in our mind.” We have here the same ambiguity as we noted in discussing Berkeley in Chapter IV . In the strict sense, it is not whiteness that is in our mind, but the act of thinking of whiteness. The connected ambiguity in the word “idea,” which we noted at the same time, also causes confusion here. In one sense of this word, namely the sense in which it denotes the object of an act of thought, whiteness is an “idea.” Hence, if the ambiguity is not guarded against, we may come to think that whiteness is an “idea” in the other sense, i.e.