  The ten categories, then, are studied both in grammar and logic, albeit in different ways, but not in metaphysics. They are studied to the extent that they signify things, but we must not suppose that there is any one-to-one correspondence between words and concepts on the one hand and things on the other. There is generally a one-to-one correspondence between words and concepts, though even here this is not always true.  For example, in his Summa logicae, he claims that participles and adjectives are distinct parts of speech according to grammar, even though they are not distinct according to logic (Ockham 1974, SL 3). Nevertheless, for Ockham, there are ten categories of words and concepts, but the extra-mental things that are signified by them are either individual substances or individual qualities.