Summa Theologica I, q. 86: What Our Intellect Knows in Material Things
Article 3. Whether our intellect can know contingent things?
Objection 1It would seem that the intellect cannot know contingent things: because, as the Philosopher says (Ethic. vi, 6), the objects of understanding, wisdom and knowledge are not contingent, but necessary things.
Objection 2Further, as stated in Phys. iv, 12, "what sometimes is and sometimes is not, is measured by time." Now the intellect abstracts from time, and from other material conditions. Therefore, as it is proper to a contingent thing sometime to be and sometime not to be, it seems that contingent things are not known by the intellect.
On the contraryAll knowledge is in the intellect. But some sciences are of the contingent things, as the moral sciences, the objects of which are human actions subject to free-will; and again, the natural sciences in as far as they relate to things generated and corruptible. Therefore the intellect knows contingent things.
I answer thatContingent things can be considered in two ways; either as contingent, or as containing some element of necessity, since every contingent thing has in it something necessary: for example, that Socrates runs, is in itself contingent; but the relation of running to motion is necessary, for it is necessary that Socrates move if he runs. Now contingency arises from matter, for contingency is a potentiality to be or not to be, and potentiality belongs to matter; whereas necessity results from form, because whatever is consequent on form is of necessity in the subject. But matter is the individualizing principle: whereas the universal comes from the abstraction of the form from the particular matter. Moreover it was laid down above (A[1]) that the intellect of itself and directly has the universal for its object; while the object of sense is the singular, which in a certain way is the indirect object of the intellect, as we have said above (A[1]). Therefore the contingent, considered as such, is known directly by sense and indirectly by the intellect; while the universal and necessary principles of contingent things are known only by the intellect. Hence if we consider the objects of science in their universal principles, then all science is of necessary things. But if we consider the things themselves, thus some sciences are of necessary things, some of contingent things.
From which the replies to the objections are clear.
Article 4. Whether our intellect can know the future?
Objection 1It would seem that our intellect knows the future. For our intellect knows by means of intelligible species abstracted from the "here" and "now," and related indifferently to all time. But it can know the present. Therefore it can know the future.
Objection 2Further, man, while his senses are in suspense, can know some future things, as in sleep, and in frenzy. But the intellect is freer and more vigorous when removed from sense. Therefore the intellect of its own nature can know the future.
Objection 3The intellectual knowledge of man is superior to any knowledge of brutes. But some animals know the future; thus crows by their frequent cawing foretell rain. Therefore much more can the intellect know the future.
On the contraryIt is written (Eccles. 8:6,7), "There is a great affliction for man, because he is ignorant of things past; and things to come he cannot know by any messenger."
I answer thatWe must apply the same distinction to future things, as we applied above (A[3]) to contingent things. For future things considered as subject to time are singular, and the human intellect knows them by reflection only, as stated above (A[1]). But the principles of future things may be universal; and thus they may enter the domain of the intellect and become the objects of science.
Speaking, however, of the knowledge of the future in a general way, we must observe that the future may be known in two ways: either in itself, or in its cause. The future cannot be known in itself save by God alone; to Whom even that is present which in the course of events is future, forasmuch as from eternity His glance embraces the whole course of time, as we have said above when treating of God's knowledge (Q[14], A[13]). But forasmuch as it exists in its cause, the future can be known by us also. And if, indeed, the cause be such as to have a necessary connection with its future result, then the future is known with scientific certitude, just as the astronomer foresees the future eclipse. If, however, the cause be such as to produce a certain result more frequently than not, then can the future be known more or less conjecturally, according as its cause is more or less inclined to produce the effect.
Reply to Objection 1This argument considers that knowledge which is drawn from universal causal principles; from these the future may be known, according to the order of the effects to the cause.
Reply to Objection 2As Augustine says (Confess. xii [*Gen. ad lit. xii. 13]), the soul has a certain power of forecasting, so that by its very nature it can know the future; hence when withdrawn from corporeal sense, and, as it were, concentrated on itself, it shares in the knowledge of the future. Such an opinion would be reasonable if we were to admit that the soul receives knowledge by participating the ideas as the Platonists maintained, because in that case the soul by its nature would know the universal causes of all effects, and would only be impeded in its knowledge by the body, and hence when withdrawn from the corporeal senses it would know the future.
But since it is connatural to our intellect to know things, not thus, but by receiving its knowledge from the senses; it is not natural for the soul to know the future when withdrawn from the senses: rather does it know the future by the impression of superior spiritual and corporeal causes; of spiritual causes, when by Divine power the human intellect is enlightened through the ministry of angels, and the phantasms are directed to the knowledge of future events; or, by the influence of demons, when the imagination is moved regarding the future known to the demons, as explained above (Q[57], A[3]). The soul is naturally more inclined to receive these impressions of spiritual causes when it is withdrawn from the senses, as it is then nearer to the spiritual world, and freer from external distractions. The same may also come from superior corporeal causes. For it is clear that superior bodies influence inferior bodies. Hence, in consequence of the sensitive faculties being acts of corporeal organs, the influence of the heavenly bodies causes the imagination to be affected, and so, as the heavenly bodies cause many future events, the imagination receives certain images of some such events. These images are perceived more at night and while we sleep than in the daytime and while we are awake, because, as stated in De Somn. et Vigil. ii [*De Divinat. per somn. ii.], "impressions made by day are evanescent. The night air is calmer, when silence reigns, hence bodily impressions are made in sleep, when slight internal movements are felt more than in wakefulness, and such movements produce in the imagination images from which the future may be foreseen."
Reply to Objection 3Brute animals have no power above the imagination wherewith to regulate it, as man has his reason, and therefore their imagination follows entirely the influence of the heavenly bodies. Thus from such animals' movements some future things, such as rain and the like, may be known rather from human movements directed by reason. Hence the Philosopher says (De Somn. et Vig.), that "some who are most imprudent are most far-seeing; for their intelligence is not burdened with cares, but is as it were barren and bare of all anxiety moving at the caprice of whatever is brought to bear on it."