25 : On the Conversion of de possibili Propositions
Conversion of de possibili Propositions cedent is true and the consequent false was stated before® when it was explained how the predicate names its form in a way different from the subject. Therefore, what was said there should be absolutely impressed upon the memory, so that one might know what is required for the truth of past-tense and future-tense propositions and for the truth of modal propositions and their equivalents,
25: On the Conversion of de possibili Propositions With respect to the conversion of de possibili propositions it should first be noted that in this chapter 'possible' is always being construed in such a way that it is common both to what is necessary and to what is contingent and not necessary. Thus, 'possible' means the same as 'a proposition which is not impossible'.
And if one takes 'possible' in this way, then it should be conceded that God is possibly God and that a man is possibly an animal.
Now, taking 'possible' in this sense, it should be noted that the same rules which were given for the conversion of de necessario propositions should be applied to the conversion of de possibili propositions. For a de possibili proposition taken in the sense of composition—or an equivalent proposition—should be converted in the same way that its non-modal counterpart is converted. For in all such conversions one argues in accord with the rule 'If one of two interchangeable propositions is possible, the other is possible', or in accord with the rule 'If the antecedent is possible, the consequent is possible'. And these rules are always true.
However, if such propositions are taken in the sense of division or are equivalent to propositions so taken, then they are not converted in the same way. Hence, this does not follow:
'God is possibly a being which does not create; therefore a being Conversion of de possibili Propositions which does not create is possibly God'—where the subject of the consequent is taken for that which is actually a being which does not create. Similarly, this does not follo v: 'A person who is living on earth is possibly damned; therefore someone who is damned is possibly living on earth'. Rather, this consequent follows: 'therefore someone who is possibly damned is living on earth'.
Nevertheless, in order to make it clearer how such de possibili propositions should be converted, it should be noted that when the subject of a de possibili proposition is a common term or includes a common term, then the proposition must be distinguished.
For the subject can supposit either for that which is actually suchand-such or for that which is possibly such-and-such. This rule should be understood "as analogous to what was said above about past-tense and future-tense propositions. Now if the subject of the antecedent is taken for those things which are actually suchand-such, then the proposition in question is converted into a de possibili proposition, the subject of which is taken for those things which are possibly such-and-such—and not for those things which are actually such-and-such. Hence, this is valid: 'Someone who is living on earth is possibly damned; therefore someone who is possibly damned is possibly living on earth'. Similarly, this follows:
'God is possibly not a being which creates; therefore a being which is possibly not a creator is possibly God'. (And not only does this de possibili proposition follow, but the corresponding non-modal proposition, with the addition 'which is possibly
. .', also follows. For example, this follows: 'God is possibly not a being which creates; therefore a being which is possibly not a being which creates is God'.) On the other hand, if the subject of the antecedent is taken for those things which are possibly such-andsuch, then that antecedent is converted into a de possibili proposition, the subject of which is taken for those things which are possibly such-and-such—and it is not converted into a non-modal
.Proposition. However, if the predicate of the antecedent is a singular term or a demonstrative pronoun standing alone, then that aintecedent is converted without qualification into a de possibili proposition. For example, this follows: 'A being which creates is possibly God; therefore God is possibly a being which creates'.
This holds whether the subject of the antecedent is taken for