Aristotle - The Organon - index for ANALYTICA PRIORIA Book 1 Part 28

To establish something about a whole, look to the subjects

Paragraph 1	If men wish to establish something about some whole, they must look to the subjects of that which is being established (the subjects of which it happens to be asserted), and the attributes which follow that of which it is to be predicated.
Paragraph 2	It is clear then that in every proposition which requires proof we must look to the aforesaid relations of the subject and predicate in question:
Paragraph 3	It is clear too that the inquiry proceeds through the three terms and the two premisses, and that all the syllogisms proceed through the aforesaid figures.
Paragraph 4	It is clear too that other methods of inquiry by selection of middle terms are useless to produce a syllogism, e.g. if the consequents of the terms in question are identical, or if the antecedents of A are identical with those attributes which cannot possibly belong to E, or if those attributes are identical which cannot belong to either term:
Paragraph 5	It is evident too that we must find out which terms in this inquiry are identical, not which are different or contrary, first because the object of our investigation is the middle term, and the middle term must be not diverse but identical.
Paragraph 6	It is clear then that from the inquiries taken by themselves no syllogism results;