Cursus Philosophicus Thomisticus, Prima Pars Artis Logicae

Supposition is defined as “the taking of a term for something of which it is verified.” Many modern authors reject this definition, supposing that supposition is only the taking of a name for the thing it signifies; they do not distinguish supposition from signification, or from the exercise of signification by which a word is substituted for a thing in signifying. Hence they reject the old and accepted principle that some propositions have a subject that does not supposit and are therefore false if affirmative, since every name, whether inside or outside a proposition, supposits simply by being substituted for something before the intellect. For Aristotle too said in On Sophistical Refutations I¹ that, because we cannot carry things with us, we use names in place of things.

Moreover, St. Thomas clearly distinguishes the signification of a name from supposition in De Potentia q. 9, a. 4, body and reply to objection 6²; the same is gathered from Summa theologiae I, q. 39, a. 5, reply to objection 5, where he admits the sophists’ rule that “substantive names supposit, while adjectives do not supposit but copulate.” Therefore, for St. Thomas, signification and supposition are not the same.

Finally, St. Thomas gave the reason for this in Sentences III, d. 6, q. 1, a. 3³, where he says: “In every name two things are to be considered: that from which the name is imposed, which is called the quality of the name, and that upon which it is imposed, which is called the substance of the name. Properly speaking, a name is said to signify the form or quality, but to supposit for that upon which it is imposed.” From this he infers in the reply to objection 1 “that a difference of supposition does not produce equivocation, but a difference of signification.” St. Thomas, then, manifestly distinguishes supposition from signification. And from his words we say that, since the signification of a name is a kind of substitution for the thing signified, substitution can be understood in two ways. In one way it is representative substitution, by which words themselves present the things signified to us; this is not supposition but signification. In another way it is applicative substitution: after the intellect has received the representation and signification of a word, it applies the name in different ways in propositions, so that the name stands for that to which it wishes to apply something. For example, when I say, “Man is white,” “man” not only represents human nature to me, but I also substitute it for that to which whiteness is to be applied through the copula “is.” The intellect therefore considers whether, with respect to such a copula, there truly and properly is a subject that is a man; if there is, it truly substitutes that subject in the proposition. If no such subject is found, the substitution is null. Thus, if I were to say, “Antichrist was good” or “Adam is white,” I do not substitute those subjects, and they do not supposit, because with respect to the copula “was,” Antichrist is not given or applied, and with respect to the copula “is,” Adam is not given. Thus these are called propositions with a subject that does not supposit.

The definition is therefore explained as follows: Supposition is “the taking of a term,” that is, a substitutive taking made by the intellect with reference to some copula in a proposition. It is understood as passive taking on the part of the term taken, not active taking on the part of the intellect that takes it. The definition adds “for something of which it is verified.” Understand this to mean: that taking of the term, or substitution, is verified for something, not that the proposition is verified of it. For the truth or verification of the proposition is not required for supposition, since supposition is found even in a false proposition. For example, when I say, “Man is a stone,” “man” supposits because something is truly found to which being a man belongs, in accordance with the demand of the copula “is.” What is required for supposition, however, is verification of the term’s taking and substitution: that what the name belongs to, and for which I substitute it with reference to the proposition’s copula, truly be found and exist in accordance with that copula’s demand.

Therefore, to confirm and show a term’s supposition, we use a proposition that demonstrates it with reference to the copula. Thus, if I say, “Man is white,” I show that “man” supposits because, with a man demonstrated in relation to the copula “is,” it is true to say, “This is a man.” In the proposition “Adam was,” “Adam” supposits because this individual, demonstrated as Adam, was at some time. And if I say, “Man is a name,” the subject’s supposition is verified by saying, “Man”—with the spoken word demonstrated—is the word “man,” or “is the word ‘man’”; and so with the rest. This demonstration, when I say “This is,” etc., need not be made to the senses; it suffices to demonstrate it to the intellect, because past and future things are not demonstrated to the senses, and the same is true of hidden things. For example, if I say, “Gold is not demonstrated,” meaning gold that is in the earth, “gold” supposits because it is verified by saying, “This (with the gold demonstrated by the intellect) is gold,” though not when demonstrated by the senses. For then the proposition would be false, as it would also be false if “not demonstrated” were not demonstrated even to the intellect. Therefore, the proposition that demonstrates supposition does not give it verification, but designates and shows it. Thus, when supposition is said to be the taking of a term for something of which it is verified, this means that it is verified of that thing in the proposition where the term is used, not in the proposition where it is demonstrated in a signified act, as one that manifests or proves supposition.

From what has been said, it follows that a term does not supposit outside a proposition. For although a term and any significant word outside a proposition signify as a term, I do not apply and substitute it for something, verifying it according to the demand of a copula, except in a proposition, where alone a copula is found and one thing is applied to another as predicate and subject. Thus applicative substitution for something, verified according to the demand of a copula—which is supposition—does not occur outside a proposition. Significative substitution, however, ordered to composing a proposition, does occur there.

It follows secondly that supposition, as explained in the definition, is defined so generally that it can also apply to adjectives when they are used adjectivally. For example, if I say, “Peter is white,” “white” is also taken for something of which it is verified and to which the notion of white belongs according to the demand of the copula. If, however, supposition is taken more narrowly to mean not only being taken for something but also supplying a subject to a verb—which is supposing in the stricter sense—then adjectives do not supposit, but copulate their formal signification to another supposit, as the ancients said.