Second figure it can only be in the minor premiss, and that only in one mode (_Camestres_) of the figure.[22] The essence of _Petitio Principii_ consists in this, that you exhibit as true _per se_ that which is not really true _per se_.[23] You may commit this fault either in Demonstration, when you assume for true what is not really true, or in Dialectic, when you assume as probable and conformable to authoritative opinion what is not really so.[24]** [Footnote 21: Ibid. p. 65, a. 1-10.] [Footnote 22: Ibid. p. 65, a. 10: [Greek: ei) ou)=n tis, a)dê/lou o)/ntos o(/ti to\ A u(pa/rchei tô=| G, o(moi/ôs de\ kai\ o(/ti tô=| B, ai)toi=to tô=| B u(pa/rchein to\ A, ou(/pô dê=lon ei) to\ e)n a)rchê=| ai)tei=tai, a)ll' o(/ti ou)k a)podei/knusi, dê=lon; ou) ga\r a)rchê\ a)podei/xeôs to\ o(moi/ôs a)/dêlon. ei) me/ntoi to\ B pro\s to\ G ou(/tôs e)/chei ô(/ste tau)to\n ei)=nai, ê)\ dê=lon o(/ti a)ntistre/phousin, ê)\ u(pa/rchei tha/teron thate/rô|, to\ e)n a)rchê=| ai)tei=tai. kai\ ga\r a)/n, o(/ti tô=| B to\ A u(pa/rchei, di' e)kei/nôn deiknu/oi, ei) a)ntistre/phoi. nu=n de\ tou=to kôlu/ei, a)ll' ou)ch o( tro/pos. ei) de\ tou=to poioi=, to\ ei)rême/non a)\n poioi= kai\ a)ntistre/phoi ô(s dia\ triô=n.] This chapter, in which Aristotle declares the nature of Petitio Principii, is obscure and difficult to follow. It has been explained at some length, first by Philoponus in the Scholia (p. 192, a. 35, b. 24), afterwards by Julius Pacius (p. 376, whose explanation is followed by M. B. St. Hilaire, p. 288), and by Waitz, (I. p. 514). But the translation and comment given by Mr. Poste appear to me the best: "Assuming the conclusion to be affirmative, let us examine a syllogism in Barbara:-- All B is A. . All C is B. . . All C is A. And let us first suppose that the major premiss is a Petitio Principii; _i.e._ that the proposition _All B is A_ is identical with the proposition _All C is A_. This can only be because the terms B and C are identical. Next, let us suppose that the minor premiss is a Petitio Principii: _i.e._ that the proposition _All C is B_ is identical with the proposition _All C is A_. This can only be because B and A are identical. The identity of the terms is, their convertibility or their sequence ([Greek: u(pa/rchei, e(/petai]). This however requires some limitation; for as the major is always predicated ([Greek: u(pa/rchei, e(/petai]) of the middle, and the middle of the minor, if this were enough to constitute Petitio Principii, every syllogism with a problematical premiss would be a Petitio Principii." (See the Appendix A, pp. 178-183, attached to Mr. Poste's edition of Aristotle's Sophistici Elenchi.)