Page:O. F. Owen's Organon of Aristotle Vol. 1 (1853).djvu/236

 does not yet beg the question, but he does not prove it. If however A and B should be the same, or should be converted, or A should follow B, he begs the question from the beginning for the same reason, for what the petitio principii can effect we have shown before, viz. to demonstrate a thing by itself which is not of itself manifest. If then the petitio principii is to prove by itself what is not of itself manifest, this is not to prove, since both what is demonstrated and that by which the person demonstrates are alike dubious, either because the same things are assumed present with the same thing, or the same thing with the same things; in the middle figure, and also in the third, the original question may be the objects of petition, but in the affirmative syllogism, in the third and first figure. Negatively when the same things are absent from the same, and both propositions are not alike, (there is the same result also in the middle figure,) because of the non-conversion of the terms in negative syllogisms. A petitio principii however occurs in demonstrations, as to things which thus exist in truth, but in dialectics as to those (which so subsist) according to opinion.