of the position. Or if this is not, the false nevertheless arises; it must not be so assumed, as if the impossible will happen from something else being laid down, but when this being subverted, the same impossible is concluded through the remaining propositions, since perhaps there is no absurdity in inferring the false through several hypotheses, as that parallel lines meet, both whether the internal angle is greater than the external, or whether a triangle has more than two right angles.
Chapter 18
False reasoning arises from what is primarily false. For every syllogism consists of two or more propositions, if then it consists of two, it is necessary that one or both of these should be false, for there would not be a false syllogism from true propositions. But if of more than two, as if C (is proved) through A B, and these through D E F G, some one of the above is false, and on this account the reasoning also, since A and B are concluded through them. Hence through some one of them the conclusion and the false occur.
Chapter 19
To prevent a syllogistical conclusion being adduced against us, we must observe narrowly when (our opponent) questions the argument without a conclusions, lest the same thing should be twice granted in the propositions, since we know that
