Kitap 7
1.80
The first kind of indemonstrable statement is that in which the whole argument is constructed of a hypothetical proposition and the clause with which the hypothetical proposition begins, while the final clause is the conclusion; as e.g. If the first, then the second; but the first is, therefore the second is.Cf. Sext. Emp. Pyrrh. Hyp. ii. 157 sq. The second is that which employs a hypothetical proposition and the contradictory of the consequent, while the conclusion is the contradictory of the antecedent; e.g. If it is day, it is light; but it is night, therefore it is not day. Here the minor premiss is the contradictory of the consequent; the conclusion the contradictory of the antecedent. The third kind of indemonstrable employs a conjunction of negative propositions for major premiss and one of the conjoined propositions for minor premiss, concluding thence the contradictory of the remaining proposition; e.g. It is not the case that Plato is both dead and alive; but he is dead, therefore Plato is not alive.
1.81
The fourth kind employs a disjunctive proposition and one of the two alternatives in the disjunction as premisses, and its conclusion is the contradictory of the other alternative; e.g. Either A or B; but A is, therefore B is not. The fifth kind is that in which the argument as a whole is constructed of a disjunctive proposition and the contradictory of one of the alternatives in the disjunction, its conclusion being the other alternative; e.g. Either it is day or it is night; but it is not night, therefore it is day.
1.81
From a truth a truth follows, according to the Stoics, as e.g. It is light from It is day; and from a falsehood a falsehood, as It is dark from It is night, if this latter be untrue. Also a truth may follow from a falsehood; e.g. from The earth flies will follow The earth exists; whereas from a truth no falsehood will follow, for from the existence of the earth it does not follow that the earth flies aloft.
