Prior Analytics - Book II   

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. How we ought to watch the middle in reference to each

conclusion, is evident from our knowing what kind of thesis is

proved in each figure. This will not escape us since we know how we

are maintaining the argument.

That which we urge men to beware of in their admissions, they

ought in attack to try to conceal. This will be possible first, if,

instead of drawing the conclusions of preliminary syllogisms, they

take the necessary premisses and leave the conclusions in the dark;

secondly if instead of inviting assent to propositions which are

closely connected they take as far as possible those that are not

connected by middle terms. For example suppose that A is to be

inferred to be true of F, B, C, D, and E being middle terms. One ought

then to ask whether A belongs to B, and next whether D belongs to E,

instead of asking whether B belongs to C; after that he may ask

whether B belongs to C, and so on. If the syllogism is drawn through

one middle term, he ought to begin with that: in this way he will most

likely deceive his opponent.



20



Since we know when a syllogism can be formed and how its terms

must be related, it is clear when refutation will be possible and when

impossible. A refutation is possible whether everything is conceded,

or the answers alternate (one, I mean, being affirmative, the other

negative). For as has been shown a syllogism is possible whether the

terms are related in affirmative propositions or one proposition is