Chapter 17
That the false does not happen on account of this, (which we are accustomed to say frequently in discussion) occurs first in syllogisms leading to the impossible, when a person contradicts that which was demonstrated by a deduction to the impossible. For neither will he who does not contradict assert that it is not (false) on this account, but that something false was laid down before; nor in the ostensive (proof), since he does not lay down a contradiction. Moreover when any thing is ostensively subverted through A B C, we cannot say that a syllogism is produced not on account of what is laid down, for we then say that is not produced on account of this, when this being subverted, the syllogism is nevertheless completed, which is not the case in ostensive syllogisms, since the thesis being subverted the syllogism which belongs to it will no longer subsist. It is evident then that in syllogisms leading to the impossible, the assertion, "not on account of this," is made, and when the original hypothesis so subsists in reference to the impossible as that both when it is, and when it is not, the impossible will nevertheless occur.
Hence the clearest mode of the false not subsisting on account of the hypothesis, is when the syllogism leading to the impossible does not conjoin with the hypothesis by its media, as we have observed in the Topics. For this is to assume as a cause, what is not a cause, as if any one wishing to show that the diameter of a square is incom-
