Chapter 22

The simplicity and oneness of the rational soul

636. If the sensitive and intellective principles are simple, and identify in the rational soul, the rational soul is simple.
In fact, as I said, myself who performs an act performs all acts. Myself who acts through the body in one space, acts in all the other spaces where it wants to act. Myself who acts at one time, acts at other times. Myself who suffers is myself who acts. Myself who feels is myself who understands; myself is always the same, one and most simple myself. Hence, myself the human rational soul, is shown to be simple and spiritual, by its perfectly constant entity amid varying accidents (cf. 140-180).

637. On the one hand, the simplicity of the soul, of every soul, is certain and manifest; on the other, the supposition that the soul is extended is seen as manifestly absurd. Nevertheless, despite the unassailable proofs that the human being is one, and can have only one soul, a kind of doubt returns to weaken our conviction about the truths we have found. The following considerations explain the origin of this doubt:

1. The proof of the unity of the human soul deduced from consciousness, that is, from the unity of myself, does not settle the doubt that outside myself but connected with it, there could be another sensitive soul.

2. Consciousness does not show that all the actions done in a human being are done by myself, and that myself is consequently the only operative principle in the human being. On the contrary, many things happen in human beings which myself cannot do, and others happen which myself directly opposes, such as the movements of our lower part pertaining to animality. Finally, certain vital actions, like the circulation of the blood, are almost entirely outside the free dominion of our rational part, and hence carried out by another principle.

3. Human beings, when acting intelligently, seem different beings when acting as animals. Sometimes, in their desire to lose themselves in sense pleasures, their intellectual functions are suspended. They could not desire this if they were merely rational souls.

4. The proof deduced from the oneness of the principle of intelligence and of sensation demonstrates only the existence of a single intellective principle, whose action is sometimes associated and identified with the animal principle (in any case, not every sensitive act must always be attributed to the principle of intellective acts). But this does not prove that the animal principle does not sometimes manifest and have its own activity. In these cases, the animal principle differs from the principle of intelligence.

Influenced by these reasons, some weighty philosophers apparently attributed two souls, one intellective, the other sensitive, to the human being. Nearly all contemporary physiologists, guided by substantially the same or similar reasons, distinguish between the human soul and the principle of animal life.

638. These difficulties are not to be despised and have some foundation, but prove nothing against the thesis of the oneness of the human soul. The question, 'Is the human soul one and simple?' differs from 'Does the soul, although one and simple, have two different activities divisible from each other, but joined in such a way that during the state and act of union, the principle of one identifies with the principle of the other, that is, they have a single principle called "soul"?'

639. The proofs I have put forward show that both questions must be answered affirmatively:

1. The proof deduced from the unity of myself demonstrates that, if something happened in the human being which could not be attributed to the intellective principle, the activity would not be another human soul. It would be an activity not pertaining to the human soul.

640. 2. The proof drawn from the fact that sensitive acts can sometimes be reduced to the understanding principle shows that in this case the principle of the two kinds of acts, sensitive and intellective, is a single principle, and that this single principle is the single human soul. Everything that remains outside this single principle therefore does not constitute a human soul.

3. I have conceded that the sensitive principle, considered in itself, differs from the intellective principle. However, I said that these two principles are capable of uniting in a single principle, not perhaps in the way that two mathematical points, having come together and united, become a single point, but at least in the way that two straight lines joined end to end, have only a single, not a double starting point.

641. 4. I said that the foundation of the union of the intellective and sensitive principles is the fundamental perception of the animal feeling. This perception is an act of the intellective principle which now acquires the title 'rational'. Indeed, granted this perception, the intellective principle becomes simultaneously sensitive, although it feels in another, higher way than the merely sensitive principle feels. The intellective principle perceives the substantial feeling (term and principle) under the nature of ens, that is, as a mode or act of ens (because the substantial feeling is itself a special actuality of being in general). Now, the intellective principle could not perceive the feeling as ens, unless it perceived it as feeling.
Hence what it perceives is feeling-ens.

On the other hand, the sensitive principle has as term that which is felt as felt, and not as ens, nor as feeling (principle and term). The sensitive principle, which is identical with the intellective principle, is precisely the intellective principle itself which, perceiving the ens-feeling, feels its term (the felt element) with a feeling enclosed in the ens, its proper object. The sensitive principle, however, in so far as it simply adheres to the extended term and producing feeling - and consequently perceives neither the ens nor itself - does not identify with the human soul and is not the human soul. It is to this principle that those movements must be attributed which are carried out in the human being without the co-operation of the intellective principle, or contrary to its will.

642. 5. In this way, the purely sensitive principle does not lose its activity, because the union is effected by means of a permanent intellective perception which does not alter the nature of the thing perceived, although it can act on it and even dominate it. Thus, the felt element can be term simultaneously of the purely sensitive principle and of the intellective-sensitive or rational principle.
This explains how two powers, that of the purely sensitive principle, and of the perceptive or rational principle, can act on the identical felt element and even come into conflict.

This also explains how the sensitive and the perceptive (or rational) principles can influence each other. If the purely sensitive principle, through its own spontaneity (granted a suitable stimulus), changes its felt element, the term of perception is also changed. In this case, it is able indirectly to modify and move the act of the rational principle. On the other hand, if the rational principle wants to change the felt element, which together with the sentient principle it actually perceives, it does so by acting directly on the sentient principle. Although perception, when actual, does not change the nature of what is perceived, the perceiving element has the force to act on it and change it. Thus, when I actually perceive an external body by touch, I can change the body because the actual perception joining it to me provides the occasion for doing so. This explains why human beings can change their own body, which they perceive directly as felt. We have therefore resolved the first, second and fourth objections.

643. 6. The third objection is concerned with people who abandon themselves willingly to sense-pleasure. We must not believe that in doing this they lose their immanent, fundamental perception (despite the suspension of their reflective acts). It is not true that sensation alone remains. Pure sensation, cut off from everything else, cannot be desired by human beings, by rational principles. In a case like this, human perception is reinforced, and the feeling comprised in the perception becomes the object of desire. It is not a question of desiring mere sensation. The first act desired among rational acts is that of intense perception, which is sought even to the point of sacrificing other reflective acts.

644. 7. Finally, it will be helpful to note that in perception the rational principle is not so much active as receptive, although it has and communicates the form, which makes it the informing cause.(339) If the fundamental perception alone is considered, it is difficult to see how the rational principle is also the principle modifying feeling. But if we go further and reflect that every actual perception endows the rational principle with an active faculty (corresponding to the receptive faculty of perception), through which it can be a cause of modification in what is perceived, we will see how the activity of the rational principle on the animal felt element is not as actual and permanent as the fundamental perception itself. The rational principle can in fact begin and end its act, and it is therefore a potency, not an act. As long as this activity of the rational principle remains in a state of potency, the sensitive principle can act independently of it and modify the animal feeling. These modifications are all received by the perceiving principle in its receptivity and informed by it, that is, they are reduced to a rational condition.

645. To these observations let me add another about Plato's definition of human being as, 'An intelligence aided by organs'. It is defective, as I have shown,(340) but here I want to discuss what is true in it, the part that suggested it to Plato's mind - the errors of great men, as I like to repeat, are simply great or subtle truths, but disguised and imperfect. Aristotle, followed by the Scholastics, found Plato's definition defective because it apparently united intelligence to the body as mover and not as form.(341) But is it entirely wrong to consider intelligence rather as mover of the body than as form?

The answer certainly depends on how we define and determine the nature of intelligence and of organic body. The definition is defective precisely because the two terms are used without this determination.

But if we replace the generic term 'intelligence' with 'intelligence perceiving animality', and organic body or 'by organs' with 'animal', the definition would be corrected and become 'an intelligence which aided by animality itself, naturally perceives animality'. In this case the relationship between this kind of intelligence and animality could be that between mover and moved, because the rational form given to animality is already expressed by this determination of the intelligence. The fact that animality occurs twice in the definition would cause no difficulty; in reality, animality, that is, substantial animal feeling, has two modes of being in humans: it is present as perceived in the rational principle, and thus informed by this principle; and it is present in itself as mere feeling, and thus moved.

646. Human beings are thus composed of two parts, one their essence, the other their condition. These two parts would be the rational soul and living body, not soul and body. In Scripture spirit and flesh seem to correspond to these two parts, because the word 'flesh' means living flesh endowed with feeling, not dead flesh.

We must now discuss the origin of the intellective soul, a question much debated by ancient philosophers and by the Fathers of the Church, but later abandoned by modern thinkers, who were exhausted by such long investigations and disheartened about finding a solution.

Notes

(339) Informing cause is not the same as active cause.

(340) AMS, 24-26.

(341) Aristotle, De Anima.