Aristotle

“ The Essence cannot be proved by the Definition of the thing itself or by that of its opposite Division supplies no common attribute by means of which the various attributes may be bound together, so as to produce one predication instead of several. Is it possible to demonstrate the real essence of a subject when one has assumed hypothetically that the essential nature of that subject is one of the properties which constitute its formal cause, and that only those particular qualities, all being peculiar to the subject, are so included? ”

“ Has one not however really used the same term, the notion of formal cause, twice over? for one must effect the proof by means of the middle term which ought itself to be proved. Further, just as in a syllogism there is no assumption as to the nature of inference, for the premises on which the syllogism is based always bear the relation of whole or of part to each other, so the essential form of syllogism ought not to be included in the syllogism, but to remain outside the particular premises. ”

“ Neither can a definition be proved by means of a hypothesis, as illustrated by the following example. Assuming that Evil consists in the quality of ‘the manifold,’ and, in the case of subjects which have an opposite, the opposite of evil, is the opposite of manifold; it might be inferred that good, as being the opposite of evil will possess the quality which is the opposite of manifold, and the essence of good will be proved to be the same as the essence of indivisible. ”