The Sentient Life-Principle

a) Nature of the Sentient Life-Principle — b) Characteristics of the Sentient Life-Principle

a) Nature of the Sentient Life-Principle

We have already seen that every bodily being is made of prime matter and substantial form. Further, the vital principle or soul of a living body is the substantial form of that body. Now, the sentient life-principle is the substantial form of the animal’s organic body. And the animal’s organic body, like the plant’s, is made of prime matter and substantial form. Therefore the sentient life-principle is the substantial form of the animal organism.

Now the sentient organism is a living body of the second grade. It is endowed with the vegetal operations (nutrition, growth, generation) and with the sentient operations (sensation, appetition, locomotion). All these operations are vital operations; they are all immanent. They all come from one and the same source — the substantial form or life-principle of the animal. The sentient life-principle is the one and only substantial form of the animal, and it is the root-source of all the vital operations. For there is not a plurality of substantial forms in the same body. The sentient soul is the one substantial form of the organism, and it is at the same time the vegetal and the sentient life-principle: it is the root-principle of both the vegetal and the sentient operations of the animal organism.

The sentient life-principle, like the vegetal, is a material soul. It is not, indeed, made or constructed of bodily parts, but it depends for its existence and its operations upon the organic body, which is material in structure. The sentient life-principle depends on matter; without the body it does not have actuality or function; therefore, it merits the designation of material.

The sentient life-principle is incomplete both as a substance and as an animal. Manifestly, it is not an animal, but an essential constituent part of an animal. Nor is it a complete substance, for it is not fitted to exist by itself, but depends upon the organic body for existence and operation. Therefore the sentient life-principle,—like the life-principle of a plant,—is “incomplete both in the order of substantiality and in the order of species.”

To sum up: If we are asked to describe the nature of the sentient life-principle, we say: (a) that it is an incomplete substance which,—joined with the organic body of which it is the first substantial act,—constitutes the sentient organism or animal as a complete, existing, functioning living body of the second grade of organisms; (b) that it is a single actuality in each organism, and is at the same time sentient and vegetal; or, more precisely, that it is the root-principle of both the vegetal and the sentient operations of the animal organism; (c) that it is a material substantial reality, in the sense that it has an essential dependence on matter for its existence and operations.

b) Characteristics of the Sentient Life-Principle

1. The sentient life-principle is simple. Like all substantial forms, the sentient life-principle is uncomposed, not made of parts, and hence not divisible into parts. The animal soul, therefore, is not made of separable parts like the organic body.

2. The sentient life-principle is actually one in the higher animals; actually multiple (and not merely potentially multiple) in the simpler animals. In the higher grades of animal life the sentient life-principle is actually one in each organism. But in the lowest and simplest animals (the unicellular organisms) the life-principle is actually multiple — actually many. This fact is evidenced by the way in which unicellular animals reproduce: they simply divide, and the two daughter-cells are separate organisms from the moment of division. We do not have here, as in the rose-bush, the actualization of a merely potential multiplicity; we have an actual multiplicity: each of the daughter-cells has its own actual life-principle from the instant of separation.

3. The sentient life-principle is generated or reproduced per accidens. Like the vegetal life-principle, the sentient soul does not come into being by itself; it comes into being with the living organism to which it belongs. In the generation or reproduction of animals, it is the entire animal that is generated. The animal itself is generated per se; the life-principle of the animal, however, is generated per accidens.

4. The sentient life-principle undergoes corruption per accidens. When an animal dies, it is the animal which undergoes corruption per se; the sentient soul perishes with the organic dissolution of the organism — it is corrupted per accidens. The soul does not itself die; but when the organism of which it is the substantial form ceases to be, the soul ceases to exist as well.

5. The sentient life-principle is educed from the potentiality of matter. This fifth characteristic follows from the material character of the sentient soul. What does it mean to be educed from matter? An eduction is not a creation, nor is it a mere rearrangement. In the generation of an animal (or of a plant), the substance takes on a new substantial character; the new substantial form — the sentient (or vegetal) soul — emerges, so to speak, from the very potentialities latent in matter. Matter, as we have seen, is pure potentiality; it has no determination of its own. But matter is capable of being actualized in many ways, and some of these potentialities of matter are actualized when a living organism comes into being. The sentient soul, being a material substantial form — dependent on matter, incomplete without it — emerges from the potentiality of matter in a way that no spiritual substance could.

In all this, we have been discussing the production and the corruption of the lower life-principles, the material life-principles, which are the respective substantial forms of plant and animal. These principles, as we have explained, are educed from the potentiality of matter, and reduced thereto at the death of the organism. But there is another life-principle found in a living body which is not material, but spiritual. This is the human life-principle or rational soul, and we shall study it in the second Part of this manual. Here we merely mention an important fact: the human soul is not educed from the potentiality of matter (for, being spiritual, it is in no sense within the possibilities latent in matter) nor is it reduced thereto when a man dies. The human soul is, in each instance, produced by the direct creative act of Almighty God, and by the same act is simultaneously infused into the body, that is, is substantially united with the body, to actualize the single human substance. When a human being dies, his soul remains in actual existence apart from the body. For the human soul is spiritual, and, although it is united in one human substance with the body (and does not merely reside in the body like a prisoner in a cell), it is not dependent on matter for its existence or those operations which are peculiarly its own.

Summary of the Article

In this Article we have studied the nature of the sentient life-principle or animal soul. We have seen that each animal has a life-principle, and that this principle is the substantial form of the animal’s organic body. We have seen that this substantial form is the root-source of all the vital operations of the animal; that it is the one and only vital principle whereby the animal lives, takes nourishment, grows, propagates, senses, appetizes, moves by local movement. We have seen that the sentient life-principle, although it is both vegetal and sentient, is, nevertheless, a principle essentially different from, and superior to, the merely vegetal life-principle of a plant. Like the plant soul, the sentient life-principle is material, since it depends for being and operation upon matter, i.e., upon the organic body of which it is the first substantial act. We have seen that the sentient life-principle is incomplete both as a substance and as an animal. We have noticed the outstanding characteristics of the vital principle of an animal, and have found that it is simple, actually one (and only in the lower animals is it potentially multiple); that it is generated and corrupted per accidens; that (like the vegetal life-principle of a plant) it is educed from the potentiality of matter, and is reduced thereto when the animal dies.