[255] Ibid. p. 139, a. 1-8.
24. Locus from the Superlative:— Suppose the affirmation to be, It is a proprium of fire to be the lightest of all bodies: this you may refute by showing that, if fire ceased to exist, there would still be some other body the lightest of all bodies. Therefore the proprium may still be predicated of something else, when its alleged subject has ceased to exist. The proprium and its subject are not reciprocating and co-extensive; therefore it is not a true proprium.[256]
[256] Ibid. a. 9-20.
VI.
We now enter on the Sixth Book, containing the Loci bearing on Definition. In debates respecting Definition, there are five points on any of which the attack and defence may turn:—[257]
1. That which the definer enunciates as a definition may not be true at all, even as a predicate of the definiend or subject to be defined; or at least not true of everything that bears the name of the subject.
2. The definiend may have been included in a genus, but not in that genus to which it rightly and specially belongs.
3. The definition given may not be specially appropriate to the definiend (i.e., it may include, not only that but, other matters besides).
4. The definition, though unobjectionable on any of the above three grounds, may nevertheless not declare the Essence of the definiend.
5. Lastly, the definition may be good in substance, but badly expressed or set out.