Prior Analytics - Book II   

related as whole and part. It is evident also that in fallacious

reasonings nothing prevents a contradiction to the hypothesis from

resulting, e.g. if something is odd, it is not odd. For the

syllogism owed its contrariety to its contradictory premisses; if we

assume such premisses we shall get a result that contradicts our

hypothesis. But we must recognize that contraries cannot be inferred

from a single syllogism in such a way that we conclude that what is

not good is good, or anything of that sort unless a self-contradictory

premiss is at once assumed, e.g. 'every animal is white and not

white', and we proceed 'man is an animal'. Either we must introduce

the contradiction by an additional assumption, assuming, e.g., that

every science is supposition, and then assuming 'Medicine is a

science, but none of it is supposition' (which is the mode in which

refutations are made), or we must argue from two syllogisms. In no

other way than this, as was said before, is it possible that the

premisses should be really contrary.



16



To beg and assume the original question is a species of failure to

demonstrate the problem proposed; but this happens in many ways. A man

may not reason syllogistically at all, or he may argue from

premisses which are less known or equally unknown, or he may establish

the antecedent by means of its consequents; for demonstration proceeds

from what is more certain and is prior. Now begging the question is

none of these: but since we get to know some things naturally

through themselves, and other things by means of something else (the

first principles through themselves, what is subordinate to them

through something else), whenever a man tries to prove what is not

self-evident by means of itself, then he begs the original question.

This may be done by assuming what is in question at once; it is also

possible to make a transition to other things which would naturally be