Aristotle

“ In Negations some final and ultimate point is reached where the series must cease If the series terminate in the case of affirmative demonstration, it will do so in negative demonstration. It will be found that demonstration may be carried out in various figures, but that the methods are limited in number so that the demonstrations are limited also. In every figure a primary or ultimate is reached of which the attribute is predicable, though the ultimate is not predicable of the attribute. ”

“ In the second figure: if all A be B, and no C be B, then no C is A. If a demonstration of this be required it may clearly be proved either by the method just mentioned, or by our present method or by the third method. ”

“ F, may be predicable of it) , and impossible also to proceed from the first term to the last, (by the ‘first term’ I mean that which is predicable of another term though no other is predicable of it) . If this supposition be correct then the process of negative demonstration will also terminate. Negation is proved in three ways: (1) According to the first figure: all C is B, but no B is A. Then from the premise CB and from any minor premise whatsoever one must proceed to ultimate knowledge, for such a premise as this is affirmative. ”