are able to frame the complex idea of [a]2 spirit. And.. .by putting together the ideas of thinking, perceiving, liberty, and power of moving [our body], we have as clear a...notion of immaterial substances, as we have of material. (Essay 11.xxiii.15) He adduces still other passages to show that the author contrasted mind [spirit] with body. He says (p. 54) that the end of religion and morality is better secured by proving that the soul is by its nature immortal, that is, immaterial. He also quotes (p. 70) this passage: That Ô all the ideas we have of particular distinct sorts of substances, are nothing but several combinations of simple ideasÕ (Essay u.xxiii.6); which he says indicates that the author believed that the ideas of thinking and willing gave a different substance from that given by the ideas of solidity and impulse. And he says that in ¤ 17 the author remarks that the latter ideas constitute body as opposed to mind. The Bishop of Worcester could have added that even if the general idea of substance is present in both body and mind, it does not follow, as our author asserts in the part of his first letter which I have presented, that their differentiae are modifications of a single thing. Modifications must be distinguished from attributes. The faculties for having perception and for acting, together with extension and solidity, are attributes, i.e. permanent main predicates; whereas thought, impetus, shape, and motion are modifications of these attributes. Furthermore one should distinguish between ¥physical (or rather real) genus and logical (or ideal) genus. Things which are of the same physical genus, or which are homogeneous \ are so to speak of the same matter and can often be transformed from one into the other by changing their modifications Ñ circles and squares for instance. But two heterogeneous things can belong to a common logical genus, and then their differentiae do not consist in mere accidental modifications of a single subject or of a single metaphysical or physical matter. For instance, 64 time and space are very heterogeneous things, and it would be a mistake to think that they have resulted from modifications of who knows what real common subject, characterized only by continuous quantity in general. Yet their common logical genus is continuous quantity. Perhaps people will laugh at these philosophersÕ distinctions: two genera, one merely logical, the other real as well; and two matters, one physical (which is that of bodies), the other merely metaphysical or general - as if