In the first place … it will be necessary to explain what an individual substance is. It is indeed true that when several predicates are attributes of a single subject and this subject is not an attribute of another, we speak of it as an individual substance, but this is not enough, and such an explanation is merely nominal. We must therefore inquire what it is to be an attribute in reality of a certain subject.‘What is a Thing (substance)?’ expresses two quite different problems. One belongs to ontology, the other to categorial ana