Cursus Philosophicus Thomisticus, Secunda Pars Artis Logicae

We said above that the pre-predicaments contain certain preliminary and prerequisite matters for establishing and distinguishing the coordination of the categories. Such prerequisites, then, are four distinctions or conditions that Aristotle sets out here. The first distinction, or first pre-predicament, is the division of univocals, equivocals, and denominatives. The second is the distinction between complex and non-complex things. The third pre-predicament is the distinction between things that are in a subject and things that are said of a subject. The fourth is the distinction between things that pertain to the direct line of the categories and things that are related laterally and indirectly; Aristotle explains it through two pre-predicamental rules. The division of being itself into the different categories does not belong to a pre-predicament; rather, it makes the categories known.

The reason for the first pre-predicament is that, to understand the ordering of the categories, we must consider three kinds of relation. The first is to predicates that stand above all the categories. The second is to things coordinated within the same category. The third is the relation of things in one category to things in another. We must likewise consider agreement or disagreement in names, because the logician deals with things only insofar as they are explained through names and concepts.

The relation of the categories to what stands above them is that of ANALOGOUS OR EQUIVOCAL TERMS, because the categories do not agree in any univocal superior. Their relation to the things ordered within the same category is that of UNIVOCAL TERMS, because it is according to the same account, and not merely according to the same name. A category’s relation to another category, in turn, is one of DENOMINATION, insofar as one is related accidentally to the other. For one category cannot be compared essentially with another: things that communicate essentially belong to the same category. It was therefore necessary to treat equivocal, univocal, and denominative terms as the first pre-predicament, explaining this threefold relation without which the categories cannot be coordinated and brought together.

The reason for the second pre-predicament is that the categories are coordinations of simple things, not of complex ones. Natures are placed in the categories, and these have a single definition and quiddity. For what lacks unity and quiddity in its essence is not being simply but many beings; unity is a property of being. In a coordination of essences, then, we must place incomplex natures, which alone are definable quiddities. Thus the DISTINCTION BETWEEN COMPLEX AND NON-COMPLEX THINGS had to be set out as another pre-predicament.

The reason for the third pre-predicament is that these series, or coordinations, of predicates in each category are established through being subject to and predicated of—that is, through superior and inferior subjects and predicates. To form these coordinations, then, we must distinguish what it is to BE IN A SUBJECT AND TO BE SAID OF A SUBJECT. Being in a subject pertains to something real, namely, an accident that inheres; being said of a subject pertains to something intentional, namely, a predicate said of something. Aristotle thus sets out four combinations. Some things are said of a subject but are not in a subject, such as universal substances, which are predicated of inferiors but do not inhere. Others have the opposite status: they are in a subject but are not said of a subject, as with singular accidents that inhere—for example, this particular whiteness—but are not predicated because they are not superior. Others are neither said of nor in a subject, such as singular substances, for example, this human being. Finally, others are both said of and in a subject, such as universal accidents, for example, white. In this third pre-predicament Aristotle therefore distinguishes two kinds of beings, substance and accident, and two kinds of intentions, universality and singularity. All of this greatly assists in forming the coordinations of the categories of accident and substance according to singularity and universality.

Finally, the reason for the fourth pre-predicament is that, in coordinating the categories, we must know both the connection among things placed in a direct line—which pertains to the proper placement of a category—and the connection or separation of things placed laterally, as differences. Aristotle thus gives two rules:

First is: Whenever something is predicated of a subject, whatever is said of the predicate is said of the subject. The sense is this: whenever something is said of a subject—that is, of an inferior, whether it is the absolute lowest subject, as an individual is, or is not altogether lowest, as a species is—whatever is universal relative to that inferior functions as its predicate. Thus, whatever is said of such a predicate, and is universal relative to that predicate, will also be said of and be universal relative to that inferior subject, which is contained under the predicate. This rule therefore helps us understand the DIRECT LINE of the categorial order, which consists of superior and universal predicates together with the inferiors contained under them.

Second, however, the rule is: Genera not placed under one another—that is, where one is not placed under the other—do not have the same essential differences. If, however, they are placed under one another, they can have the same differences, that is, they can share superior differences, because those differences constitute superior genera and descend with them to inferiors. Genera can be understood as placed under one another in two ways: either one is placed under the other, or both are placed under a third, as animal and plant are not placed one under the other but both are placed under living thing. Therefore, for genera to lack the same differences absolutely and in every way, they must be placed under one another in neither way and, consequently, must belong to different categories. For if they fall under one third genus, they at least share the same difference of that genus. But since one does not share the difference of the other, while both share the superior difference of the genus under which they are contained as under a third, they are not said to have the same differences as though these were communicated from one genus to another, but as derived from one superior third genus.

We must carefully observe, however, that different genera can have similar differences by which they are divided. For example, power is divided into cognitive and appetitive as two genera, and each of these into corporeal and spiritual. Conversely, spiritual power can be divided into cognitive and appetitive; quantity is divided into continuous and discrete, and each of these into successive and permanent. Likewise, a proposition is divided into categorical and hypothetical, and each of these into affirmative and negative. But if these differences are essential and formal, although they may seem similar, they are in fact distinct and cannot be of the same account. This is clear because they formally constitute diverse natures; therefore, they cannot be of the same account. Hence St. Thomas’s general rule in Summa Theologiae I–II, q. 72, a. 5: “A difference that constitutes diversity of species is never found except in diverse species,” as rational and irrational, animate and inanimate, can never be found except in diverse species. “A difference, however, that does not constitute diversity of species, but is found in diverse species, is not incompatible with its also being found in things of the same species,” as whiteness and blackness are found in both the swan and the raven, which are diverse species, and also in two human beings. Thus, if the differences just mentioned are constitutive and essential, they can be similar but are not the same. For example, corporeal and spiritual as divisions of powers are not the same corporeal and spiritual as divisions of substances. And even among qualities and powers, corporeal and incorporeal are found under different accounts: the spirituality of the appetitive power differs from that of the intellective power. Likewise, affirmation and negation differ in categorical and hypothetical propositions, although each pair divides its respective kind of proposition. Two-footed and four-footed, however, are not differences that constitute a thing per se, but are accidental, as we said above from St. Thomas. Therefore, differences that constitute per se and formally are never of the same account in diverse genera or species.