Cursus Philosophicus Thomisticus, Secunda Pars Artis Logicae

Premises can be taken either formally or objectively. Formally, they are the acts of assent of the intellect itself by which we judge the propositions; objectively, they are the things themselves attained by assent and proposition. Logic arranges the objects themselves with respect to the connection they have, either as predicate and subject or as inferent and inferred, and presents them to the intellect, because it deals with things already known. The whole difficulty lies in arranging and attaining those things, not in really producing and ordering the cognitions themselves. Speaking in this sense, the Philosopher said in Physics II,¹ lecture 5 in St. Thomas,² that the premises contribute materially to the conclusion—that is, they provide the matter out of which it is made, because the terms of which the conclusion consists must already be had in the premises.

Now, therefore, THE ENTIRE DIFFICULTY concerns the formal premises themselves, that is, the assents to the premises: do they contribute in some kind of cause to the assent and inference of the conclusion? A similar difficulty often arises about how one act of the will is the cause of another, as intention is of choice; see I-II, qq. 9 and 12.

It is agreed by all that there is some dependence and connection between assent to the premises and assent to the conclusion, since the Philosopher says that all teaching and learning arise from pre-existing cognition—that is, a conclusion proved from a cognition that proves it. The intellect is moved from assent to the premises to assent to the conclusion, just as it moves from willing the end to willing the means.

It is also clear that final and material causes have no place in these assents. For even if the object or truth about which assent to the premises is concerned were the end, or provided matter, for the object of the conclusion, the act that concerns the object of the premises is neither the end nor the matter of the act or formal assent that concerns the conclusion, just as the act of intending is not the end of the act of choosing.

As for formal and efficient causation, some hold that the premises contribute as an extrinsic formal cause, as though specifying the conclusion, because the entire specification of assent to the conclusion is taken from the middle term of the demonstration; and when the intellect presents the premises, it properly acts only by specifying and determining. The foundation of this opinion is that it is not clear how one act of the intellect could cause another unless it left behind some determination by which the power proceeds to another act. On this view, the act itself does not contribute efficiently; rather, it is the power determined and applied by the act that does so.

HOWEVER, THE COMMON OPINION assigns efficient causation to the acts of the premises with respect to the act of the conclusion.

This is drawn from St. Thomas. In Posterior Analytics I, lecture 3,³ he says that the premises have the character of an efficient and active cause with respect to the conclusion. In Physics II, lecture 5,⁴ and Metaphysics V, lecture 3,⁵ he says that “as regards the power of inference, the premises have the character of an efficient cause.” Finally, in Summa theologiae I, q. 14, a. 7, he teaches that the reasoning by which we arrive at conclusions through principles is reasoning according to causality.

The FOUNDATION of this opinion follows from this: if the principles are related to the conclusion through reasoning according to causality, they must influence assent to the conclusion, insofar as the light of the premises so affects and determines the intellect that it manifests the conclusion to it and makes it assent by illuminating it. External light, present in a luminous body and diffused through a medium, causes the illumination of an object and efficiently determines us to its cognition. Therefore the premises, which cause the conclusion through reasoning by illuminating it as an external medium to the conclusion, efficiently influence assent to the conclusion.

Nor can one say that reasoning resembles motion, in which we pass from one thing to another, though one part of the motion does not produce another; so too, we pass from premises to conclusions as from one part of a motion to another, not as from an efficient cause to its effect. Some have thus said that assent to the premises stands as a starting point with respect to the conclusions. But this fails to distinguish reasoning according to succession from reasoning according to causality. Reasoning according to causality does not signify merely the succession of one cognition after another, as the parts of a motion are related; it also signifies the character of what illuminates, insofar as one proceeds from what is better known to what is less known. Consequently the premises determine the intellect by illuminating for it the manifestation of the inferred conclusion. They therefore cannot stand like a part of a motion that is left behind so that another part can be acquired, as a starting point stands in relation to an endpoint. Rather, this reasoning posits an inferential and manifestative power of the conclusion. Thus, insofar as they infer, the premises are not left behind by the intellect so that it may acquire the conclusion, as a starting point is left behind so that another may be reached. The premises themselves give the intellect a power—that is, a light—to acquire the conclusion; a place that is left behind does not give the motive power for reaching another place.

Nor can one say that assent to the premises influences the conclusions as a formal cause—not as their intrinsic form, but as an extrinsic form determining the intellect to the conclusions. Against this, an extrinsic form is either an object or an exemplary idea. Assent to the premises is not an idea of the conclusion, since the conclusion is not formed after their likeness, even though it is deduced from them through an intrinsic connection. Rather, assent to one premise leads the intellect to assent to another by manifesting it, not through imitation. Moreover, an idea needs the efficacy of a will that moves it in order to carry out its formation, since it causes in a practical mode. The premises, however, influence the conclusion in a purely speculative mode, without the influence of the will; the intellect is said to be moved to conclusions by the force of the premises, not by the will. But the intellect moves itself efficiently from one thing to another; therefore that moving force is efficient as well. Much less is assent to the premises an objective cause of the conclusions, since the conclusion has its own object, distinct from the premises and their assent, by which it is specified—namely, the truth that is inferred.

Whether the premises must actually exist together when the conclusion is inferred will be discussed in the following article. There, from St. Thomas, Posterior Analytics I, lecture 2,⁶ we shall show that in a demonstration the minor premise exists at the same instant as the conclusion, while assent to the major premise may precede it in time.

THE ARGUMENTS ARE ANSWERED.

First, it is argued: The whole efficient power of any cognition belongs only to the faculty, a habit added to it, or a species. One act is not operative of another act, although it can determine the faculty to another act. But assent to the premises is neither a faculty nor a habit nor a species, but an act of the intellect. Therefore it does not give the intellect efficient power to influence the conclusion.

It is confirmed as follows: the principles have the character of an extrinsic formal cause from which the specification of a science is taken. A different formal character of science is taken from a different middle term that proves or demonstrates, as St. Thomas affirms in II-II, q. 1, a. 1. Therefore the premises, which determine the intellect by means of the middle term that proves and illuminates the conclusions, function as their extrinsic formal account.

THE REPLY is that, although the intellect is the principal, universal efficient cause of assent to the conclusion, because the intellect proceeds inferentially from one thing to another it derives this inferential power from assent to the premises, in which the conclusion is virtually contained as something manifestable in what manifests it. When it is said that one act is not operative of another, a distinction must be made. If one act virtually contains another, it can produce that act by determining the faculty and giving it the power to move itself from one thing to another; but it cannot do so if it does not virtually contain the other act. We see this in the will: an act of intention causes an act of choice, and an act of command has the commanded act as its effect. St. Thomas also lists peace and joy among the effects of charity, in II-II, qq. 28 and 29, and joy as an effect of devotion, in II-II, q. 82, a. 4. For this reason an act of a virtue is distinguished from its effect: the act is elicited immediately, while the effect is commanded through another act. One act is said to determine and move to another insofar as the prior act concerns an object under which the object of the other act is virtually contained. Thus, by the very fact that the power is ordered by such an act to an object, the act has within itself the power to determine the faculty to an object contained under that one. And through this ordering or determination left by such an act—whether it is left by some impressed mode or by some species representing the past act—the faculty is moved and determined to proceed to another act.

In reply to the confirmation, the premises provide the specifying middle term if they are taken on the side of the object known, since the object specifies and formalizes the act. But on the side of the assent by which that object is known, there is no contradiction in its efficiently influencing the faculty by ordering it to the eliciting of another act and, as an interior light, formally illuminating it—that is, by inhering within it, not objectively.

Second, it is argued: If the premises efficiently influence the conclusion, it follows that assent to the premises must exist at the same time as assent to the conclusion is elicited, since an efficient cause influences only while existing. But this is false, because cognition of the premises passes away when the conclusion arrives: through reasoning and movement we pass from one thing to another, and the intellect cannot understand many things at once, as St. Thomas teaches in Summa theologiae I, q. 85, a. 4. It further follows that the minor cannot be known at the same time as the conclusion, contrary to what the Philosopher teaches in Posterior Analytics I, chapter 1,⁷ and St. Thomas there, lecture 2,⁸ since two cognitions cannot occur together, for we cannot understand many things as many. But if there is not a double cognition, neither is one efficient in another. Then at least one premise, namely the minor, does not influence the conclusion efficiently. The major alone, without the minor, cannot efficiently influence the conclusion, because the arrangement of the premises is not present in the major alone.

The second difficulty is that if the principles are the efficient cause of the conclusion, they cannot be its univocal cause, since assent to principles is of a different species from assent to conclusions, as arising from habits of different species. Therefore they will be an equivocal cause with respect to the conclusion. This cannot stand, because an equivocal cause is not proximate and immediate but universal; yet nothing intervenes between the premises and the conclusions.

Finally, if the premises are an efficient cause, God could supply their efficiency in producing the conclusion, and thus a conclusion would be inferred without the premises, which is impossible.

THE REPLY to the first difficulty is that the influencing cause exists when the conclusion is inferred, because the minor and the conclusion are known at the same time, although the minor is prior by nature, as St. Thomas teaches from the Philosopher in Posterior Analytics I, lecture 2,⁹ This is understood of the minor insofar as it virtually contains within itself the major, which it determines; this will be discussed in the following article. Nor does reasoning require that one act pass after another in temporal succession, but rather in the succession or causality of cognitions and objects, although both cognitions endure at the same time. If, however, the inferring cognition does not remain in act, it will remain virtually, in the determination by which it determines the intellect to infer the conclusion. Nor does St. Thomas deny that many things can be known at once with temporal simultaneity; he denies that they can be known with simultaneity of cognition and representation when they are not ordered or united under some aspect, but are disjoined and separate from one another. Thus, although the minor and conclusion are known at the same time, the minor can nevertheless be the efficient cause of the conclusion, because it is prior by nature though simultaneous in time, and is a distinct act.

To the second difficulty it is said that the premises are the efficient cause of the conclusion by way of a power and an instrument. An equivocal instrumental power can be immediate and proximate with respect to its effect, just as heat in an animal generates flesh, and light generates heat, immediately and proximately. As for how these assents or acts attain the conclusion by some action, about which some have doubts, the reply is that they do not attain it by any transient action, but by the very immanent action through which the conclusion proceeds from the intellect. It also proceeds efficiently from the habit as assisting, and from the actual assent to the premises as from a light that presently illuminates and provides the faculty with efficient and determining power.

To the final difficulty it is said that not every efficiency can be supplied by God in every mode—namely, when the efficiency imports or connotes some special mode or dependence under which God cannot act. Thus God can produce a human being, but cannot generate bodily as a father; and he can concur in reasoning, but cannot reason. Similarly, he cannot produce a conclusion as inferred without the premises.