Prior Analytics - Book II   

is due to the thesis to be proved and the premiss through which it

is proved being equally uncertain, either because predicates which are

identical belong to the same subject, or because the same predicate

belongs to subjects which are identical, the question may be begged in

the middle and third figures in both ways, though, if the syllogism is

affirmative, only in the third and first figures. If the syllogism

is negative, the question is begged when identical predicates are

denied of the same subject; and both premisses do not beg the question

indifferently (in a similar way the question may be begged in the

middle figure), because the terms in negative syllogisms are not

convertible. In scientific demonstrations the question is begged

when the terms are really related in the manner described, in

dialectical arguments when they are according to common opinion so

related.



17



The objection that 'this is not the reason why the result is false',

which we frequently make in argument, is made primarily in the case of

a reductio ad impossibile, to rebut the proposition which was being

proved by the reduction. For unless a man has contradicted this

proposition he will not say, 'False cause', but urge that something

false has been assumed in the earlier parts of the argument; nor

will he use the formula in the case of an ostensive proof; for here

what one denies is not assumed as a premiss. Further when anything

is refuted ostensively by the terms ABC, it cannot be objected that

the syllogism does not depend on the assumption laid down. For we

use the expression 'false cause', when the syllogism is concluded in

spite of the refutation of this position; but that is not possible

in ostensive proofs: since if an assumption is refuted, a syllogism

can no longer be drawn in reference to it. It is clear then that the

expression 'false cause' can only be used in the case of a reductio ad