Aristotle - The Organon - index for ANALYTICA PRIORIA Book 2 Part 19

Do not allow the same term twice in premisses

Paragraph 1 In order to avoid having a syllogism drawn against us we must take care, whenever an opponent asks us to admit the reason without the conclusions, not to grant him the same term twice over in his premisses, since we know that a syllogism cannot be drawn without a middle term, and that term which is stated more than once is the middle.
Paragraph 2 That which we urge men to beware of in their admissions, they ought in attack to try to conceal.

UPHOME HTML by RBJ created 1996/11/25 modified 2009/04/26