A. What there Can and Cannot be a Definition of

181. As to the first, one must note that anything at all (whether being or nonbeing) that can be conceived and signified can have some account given of its name, which name would make explicitly and distinctly explicit what the name implicitly and confusedly means, and any such account can be called a definition. So Metaphysics 4.7.1012a23-24, “The account that a name signifies is a definition,” by extension of the name ‘definition’. But a definition strictly speaking is only a statement signifying the true ‘what it is to be’ of a thing (Topics 1.4.101b39, “Now a term, that is, a definition, is a statement signifying the ‘what it is to be’,” that is, of the thing defined). And so not any account of a name is a definition, but an account by which is distinctly indicated the true ‘what it is to be’ of a thing.

182. There is no definition properly of non-being, and that whether ‘non-being’ is taken properly for what is impossible (which includes contradiction) or for what is pure negation or privation, because non-being does not have a ‘what it is’.

183. Nor is there an account either of that which is not per se one, as is plain in Metaphysics 7, as was argued for the opposite [n.175]. But by ‘per se one’ I mean either what is simple or what is composed of what is per se actual and per se potential. Nor does this unity prevent the defined thing from including in it something as the term per se of its dependence (as accident includes substance, or as something that is naturally simultaneous with it the way relative includes correlative). But what is prevented is that nothing is included in it as a per se part that is not disposed to something else in the same thing (as per se act is disposed to per se potency, or as a part of the same act, or of the same potency, to another part).

184. Nor, third, is there a definition of a being of reason, which is only a diminished being, because a ‘what’, just as also being, only properly belongs to real being, as is plain in Metaphysics 5.7-8.1017a22-7b26, 6.2.1026a33-35. And I do not mean here by ‘being of reason’ what is in the intellect as object (for thus every universal is in the soul), nor what is only in the intellect as in a subject (for thus intellection and knowledge are in the soul, which knowledge, however, and consideration are real forms and in the genus of quality). But I mean by being of reason a being in the soul as considered secondarily, and not as considered primarily (and to this consideration the soul is first moved by something outside); rather I mean a being in that which is primarily a considered thing qua considered. And such, to speak summarily, is only a relation of reason, because nothing has being precisely in being considered qua being considered, save the comparison by which the considered thing is compared to something else by the act of the considerer. So diminished being, as it is taken here, is universally a being of reason.

185. Fourth, there is no ‘what’, expressible in a definition, in the case of something that one can only have a simply simple concept of, for according to the Philosopher, Metaphysics 8.3.1043b25-26, “a definition is a long statement” and “the term must be a long statement” expressing the ‘what’ and the ‘what sort of’; for a definition distinctly explains what the defined thing implicitly imports. Therefore it must be the case that more than one concept can be formed of the defined thing, namely a quidditative and a qualitative concept, by which the defined thing is explained.

186. Fifth, definition is not of a singular, because there cannot be a statement expressing the quiddity of a singular without that statement explaining something that does not belong to the ‘what it was to be’, as is plain in Ord. II d.3 nn.192-193, 204-206.

187. From these points follows that a definition properly speaking is of a positive being [n.182], that is per se one [n.183], real [n.184], really composite [n.185], at least as to the universal concept and as to such alone [n.186].