Part II, Chapter 8: Of Complex Propositions in relation to Affirmation and Negation, and of Modals
PROPOSITIONS “WHICH PHILOSOPHERS CALL Modals.
BESIDE the propositions of which the subject, or the attribute, is a complex term, there are others which are complex, because they have incidental terms, or propositions, which regard only the form of the proposition, that is to say, the affirmation, or negation, which is expressed by the verb: as, if I say,—I maintain that the earth is round—I maintain is only an incidental proposition, which must be a part of something in the principal proposition. Yet, it is clear that it makes no part either of the subject or the attribute, for it makes no change in them at all; and they would be conceived in precisely the same way, if I said, simply, the earth is round. And thus it can belong only to the affirmation, which is expressed in two ways, the one, which is the usual, by the verb is,—the earth is round, and the other more expressly by the verb I maintain.
In the same way, when it is said, I deny that it is true, it is not true; or when we add in a proposition that which supports its truth: as when I say—the reasons of astronomy convince us that the sun is much larger than the earth; for that first part is only a support of the affirmation.
It is, nevertheless, important to notice that there are some of these kinds of propositions which are ambiguous, and which may be differently taken, according to the design of him who utters them: as if I say,—all philosophers assure us that heavy things fall downwards of themselves. If my design is to show that heavy things fall downwards of themselves, the first part of this proposition would be incidental, and would serve only to support the affirmation of the last part; but if, on the contrary, my design is merely to express this as the opinion of philosophers, without affirming it myself, then the first part will be the principal proposition, and the last would be only a part of the attribute. For what I should affirm would not be that heavy things fall of themselves, but simply, that all philosophers maintain this: and it is clear that these two different ways of taking this same proposition, so change it, that it constitutes two different propositions which have altogether different meanings. But it is generally easy to determine by the context which of these two senses we are to take. For example, if, after having uttered that proposition, I were to add—now stones are heavy—it would be clear that I had taken it in the first sense, and the first part was only incidental; but if, on the contrary, I were to conclude thus—now this is an error, and, consequently, it is possible that an error may be taught by all philosophers—it would be manifest that I had taken it in the second sense, that is to say, that the first part was the principal proposition, and that the second was only part of the attribute.
Of these complex propositions, where the complexity falls on the verb, and not on the subject or the attribute, philosophers have specially noticed those which have been called modals, because the affirmation or negation has been qualified in them by one of these four modes,—possible, contingent, impossible, necessary. And, since each mode may be affirmed or denied, as it is impossible, it is not impossible, and, in both respects, may be joined by a proposition, affirmative, or negative, as, the earth is round, the earth is not round—each mode may have four propositions, and, the four together, sixteen, which have been denoted by these four words: Purpurea, Iliace, Amabimus, Edentuli,—the whole mystery of which is, that each syllable denotes one of the four modes.
First—possible.
Second—contingent.
Third—impossible.
Fourth—necessary.
And the vowel which is found in each syllable, which is either A, or E, or I, or U, points out whether the mode ought to be affirmed or denied, and whether the proposition which is termed dictum ought to be affirmed or denied in that way.
A.—The affirmation of the mode, and the affirmation of the proposition.
E.—The affirmation of the mode, and the negation of the proposition.
I.—The negation of the mode, and the affirmation of the proposition.
U.—The negation of the mode, and the negation of the proposition.
It would only be loss of time to bring examples which may easily be found; it is only necessary to observe, that Purpurea answers to A of complex propositions, Iliace to E, Amabimus to I, Edentuli to U; and that thus if we wish our examples to be true, we must, having found a subject, take for Purpurea an attribute which may be universally affirmed of it; for Iliace one which may be universally denied of it; for Amabimus one that may be particularly affirmed of it; and for Edentuli one that may be particularly denied of it.
But whatever attribute may be taken, it is always true that all the four propositions for the same word have only the same sense, so that one being true, all the rest are