22: On the Conversion of Past-Tense and Future-Tense Non-Modal Propositions
Conversion of Pastand Future-Tense Propositions to be converted are in the nominative case—it is necessary to resolve the verb into its participle and the verb 'is'. And so it is necessary to make some change in the words over and above the transposition. of the terms. Thus, the proposition 'An altered thing is running quickly' should not be converted into 'therefore a running thing is altered quickly'. For assume that the same thing is altered slowly and is running quickly. In that case the antecedent is true and the consequent false. Rather, it should be converted into 'therefore a thing running quickly is an altered thing'—so that 'quickly' is a determination of the participle 'running' and not of the verb 'is'. Similarly, the proposition 'A being which creates is always God' should not be converted into 'therefore God is always a being which creates'.
Rather, it should be converted into 'therefore something which is always God is a being which creates'.
22: On the Conversion of Past-Tense and Future-Tense Non-Modal Propositions With respect to the conversion of past-tense and future-tense propositions it should first be noted that every past-tense or future tense proposition in which the subject is a common term must be distinguished as equivocal in the third mode. For if the propositian is past-tense, then the subject can supposit for that which is such-and-such or for that which was such-and-such. That is, such a proposition is equivocal because the subject can supposit for that of which the subject is truly predicated by means of a present-tense verb, or it can supposit for that of which the subject is truly predicated by means of a past-tense verb. For example, the proposition 'A white thing was Socrates' must be distinguished, since 'white thing' can supposit either for that which is white or for that which was white. On the other hand,
Conversion ofPastand Future-Tense Propositions if the proposition is future-tense, then it should be distinguished because the subject can supposit for that which is such-and-such or for that which will be such-and-such. That is, it can supposit for that of which the subject is truly predicated by means of a present-tense verb, or it can supposit for that of which the subject is truly predicated by means of a future-tense verb. This rule should be understood to apply when the subject supposits personally, i.e. significatively.
Second, it should be noted that when the subject of such a proposition supposits for that which is such-and-such, then the proposition in question should be converted not into a pasttense proposition, but rather into a present-tense proposition in which the subject is taken with the verb 'was' and the pronoun 'which'. Hence, this consequence is not valid, if the subject of the antecedent is taken for what is white: 'No white thing was a man; therefore no man was white'. For suppose that many men, both living and dead, were white, and that many other things were white and are now white, and that no man is now white. In that case the antecedent is true and the consequent false. For 'Nothing which is white was a man' is true, since each of its singulars is true in the assumed case. But 'No man was white' is false no matter how the subject is taken. Therefore, the proposition in question should not be converted in the way proposed above.
Rather, it should be converted as follows: 'No white thing was a man; therefore nothing which was a man is white'. And in the same way the converse follows: 'Nothing which was a man is white; therefore no white thing was a man'—where the subject of the consequent supposits for those things which are white and not for those things which were white. If, on the other hand, the subject in such a proposition is taken for that which was such-andsuch, then the proposition is converted simply into a past-tense proposition and not into a present-tense proposition. For if the subject of the antecedent is taken for what was white, then this follows: 'No white thing was a man; therefore no man was white'— this is so as long as the subject of the consequent is taken for that which was a man. For it is impossible that some man was white and yet that nothing which was white was a man.
Now if such a past-tense proposition is a singular proposition Conversion ofPastand Future-Tense Propositions in which the subject is a demonstrative pronoun standing alone or a proper name, then the proposition is converted either into a singular proposition, a universal proposition, or a particular or indefinite proposition—with the subject of the consequent being taken for that which was such-and-such. Hence, this is valid:
'Socrates was not white; therefore nothing which was white was Socrates'. But if the subject of the consequent is taken for that which is white, then the consequence is not valid. For this does not follow: 'Socrates was not white; therefore nothing which is white was Socrates'; nor does the corresponding present-tense proposition follow, namely, 'No white thing is Socrates'. For suppose that Socrates is now white for the first time. In that case 'Socrates was not white' is true, while both of the proposed consequents are false.
It should also be noted that just as such a proposition is distinguished when the subject is a common term, so also it can be distinguished when the subject is a demonstrative pronoun with a common term. Thus, the proposition 'This white thing was
Socrates' should be distinguished, since either the implied clause has a present-tense verb, in which case the proposition has this sense: 'This thing, which is white, was Socrates'; or the implied clause has a past-tense verb, in which case the proposition has this sense: 'This thing, which was white, was Socrates'. And such a proposition is converted just like a past-tense proposition in which the subject is a common term.
As far as the distinction just noted is concerned, what was said of a past-tense proposition should be applied, mutatis mutandis, to a future-tense proposition.
It should also be noted that, as was pointed out above,' in present-tense propositions an adverbial determination should, in the consequent, be added not to the main verb, but to the participle of the antecedent's verb. The same thing should be done in these past-tense and future-tense propositions.
From what has been said it is clear that consequences such as the following are not valid: 'God was not always a being which creates; therefore a being which creates was not always God'. For the antecedent, namely, 'God was not always a being which creates', is true, since he was not creating before the creation of the Conversion ofPastand Future-Tense Propositions world; but the proposition 'A being which creates was not always God?' is false, since this being which creates was always God."? For just as 'A white thing was black' is true even though 'A white thing is black' was never true, so also 'A being which creates was always God?' is true even though 'A being which creates is God' was not always true. And thus the consequence alluded to above is not valid. Rather, the proposition in question should be converted as follows: 'God was not always a being which creates; therefore nothing which was always a being which creates is God', or 'therefore nothing which was always a being which creates was
God'. And the consequent is true, since it has two causes of truth: either nothing was always creating, or something was always creating and yet is not God. The first cause is true, although the second is false. Similarly, this consequence is not valid, if the subject of the antecedent is taken for that which is with sight:
'No one with sight was blind; therefore no one blind was with sight'. Rather, the antecedent should be converted into 'No one who was blind is with sight'. And so when the subject is taken for that which is such-and-such, a past-tense proposition is converted into a present-tense proposition in the way noted above.
In the same way, when the subject is taken for that which was such-and-such, such a proposition is converted into a past-tense proposition, the subject of which is taken for that which was such-and-such..
The same holds for propositions such as 'Nothing impossible will be true'. If the subject is taken for that which is impossible, then the proposition is converted into a present-tense proposition in the following way: 'Nothing impossible will be true; therefore nothing which will be true is impossible'. If the subject is taken for that which will be impossible, then the proposition is converted into 'therefore nothing true will be impossible'—with the subject of the consequent being taken for that which will be true.
It should also be noted that if the subject of such a pastor future-tense proposition is a common term or includes a common term with a demonstrative pronoun, and if the predicate is a demonstrative pronoun standing alone or a proper name, then if the subject is taken for that which is such-and-such, the