Cursus Philosophicus Thomisticus, Secunda Pars Artis Logicae

Having completed in the first part of Logic what pertains to the form of reasoning and to prior resolution, it remains, for the completion of the whole art, to treat in this second part its matter, which pertains to posterior resolution. This treatment is longer and more extensive because the matter of an art usually has more to be treated than its form.

It should therefore be noted that every judgment of the mind is a kind of resolution or assent, and, if it is ultimate, is as it were a definitive sentence. It is given with certainty and firmness when, through its proofs, it is resolved into its principles, with which it has a connection. As we said in the first part of the Summulae¹ from St. Thomas, Posterior Analytics I, lecture 1², the firmness of judgment is taken either on the side of the form of reasoning or on the side of its matter. On the side of form, insofar as the conclusion rests on the right arrangement and connection of premises for inference, which is usually called consequence or argumentation; hence the goodness or firmness of the consequence is required for the right resolution of judgment. On the side of matter, resolution proceeds through necessary propositions connected per se to principles known per se, from which demonstration is drawn; and these are treated in this second part of Logic. The topics, which treat of the probable, and the books of the Sophistical Refutations, which treat of the sophistical part, are omitted here, since they do not treat of certain and perfect resolution of judgment. Therefore Aristotle calls only the books of the Prior and Posterior Analytics analytic, that is, resolutory, because only in them is the firmness and certainty of resolution taught, both prior resolution on the side of form and posterior resolution on the side of matter.

Since the matter required for demonstration, or certain resolution, consists of necessary propositions that hold per se, and those propositions hold per se in which essential predicates or proper attributes are predicated, because only these have a necessary connection with the subject, as is clear from Posterior Analytics I, chapter 2³, whereas propositions with accidental predicates are contingent, the suitable way of finding this necessary matter that holds per se is to explain the arrangements of the categories. In them all things are reduced to their heads and genera, and in each are placed higher and lower predicates, among which an essential connection is found; for the definition of a thing is composed from these. Likewise, the properties of each category are manifested, or at least the categories are set out in which the properties of each nature are placed. Thus we can gather at least in general the matter of propositions and their necessary connections, since knowing these in particular belongs to the particular sciences.

Again, since the categories, which are arrangements of genera and species, cannot be known unless the predicables themselves are known—which are modes of essential or accidental predication, in quid or in quale—the whole matter of the art of Logic treated in this second part is contained in these three, namely:

The predicables, which are modes of predicating and distinguish the essential and quidditative mode from the accidental or qualificative mode; then the ten categories, to which, as ten classes and highest genera, all the natures of things, their grades, and their essential predicates are reduced; and finally the books of the Posterior Analytics, in which one learns to form necessary propositions that hold per se and to make scientific demonstrations.

Although many matters treated concerning the categories, universals, and predicables belong to Metaphysics, and therefore should be treated briefly and soberly by the logician, more time is nevertheless spent disputing these matters than expounding the books of the Posterior Analytics themselves. This is not surprising, since more time is usually spent preparing things than bringing them to the final perfection for which they are ordered. Thus, among intelligible things, one reaches the final, very brief judgment through many acts of reasoning; and in natural things, substantial generation is completed in an instant, while accidental alteration prepares for it over a long time.

Before undertaking to explain, in the stated order, the matters that pertain to the object of Logic, we shall first set out a preliminary question about the science of Logic itself, so that, having come to know the science, we may more easily come to know its object.