ART. I. -- LIFE IN GENERAL.
40. A living being is one that produces or is capable of producing immanent action. -- Immanent action is action which proceeds from a principle intrinsic in the subject, and which does not go outside the subject. But life, considered as the principle of operation in a living being, manifests itself by immanent action; and considered as a substantial element of a living being, it produces, or is capable of producing, immanent action.
41. The lowest degree of life is found in plants, a higher degree in animals, a still higher degree in rational beings, and the highest degree in God. -- Two things are necessary to constitute immanent action. First, the action must proceed from an intrinsic principle; secondly, it must not go out of the subject from which it proceeds. From these two points of view the life of plants is the least perfect. For in action we may consider (1) the execution; (2) the form which determines the agent; and (3) the end to which the operation tends. Now a plant is active in itself in regard to the first only of these three things; but it does not predetermine the end of its action, nor does it acquire by its own power the form which immediately influences it to act. It is God who has assigned its end, of which, however, the plant has no knowledge; and nature gives the form by which it is determined to act, although it cannot direct the influx of that form. If we regard immanence of action under the second aspect, the action of the plant, it is true, remains in the plant; but not in the faculty that acts. The nutritive molecules absorbed through the roots and leaves do not remain in the roots and leaves, but feed the whole plant. -- The life of animals is higher than that of plants. On the one hand, since brutes act in virtue of a knowledge acquired through the senses, they in some sort give themselves the form that immediately determines their action; on the other hand, the act of sensation, which is proper to them, remains not only in the subject, but also in the faculty that produces it. Still, on account of the necessary concurrence of the material organ, this act does not remain in the vital principle only, but in the sense or organ, that is, in the composite, to which sensation properly belongs. -- In rational and intellectual beings immanence of action is perfect. The end of the action is not imposed on them by nature as in the ease of animals; but they determine it and choose it themselves. Besides, the intellectual act not being exercised with the concurrence of a material organ, it belongs entirely to the intellectual faculty alone. Nevertheless, it is only in God and not in created intelligences, that action attains the highest degree of immanence. For the action of a created intelligence proceeds from a substantial principle that holds its being from God. Besides, in created intelligences the action and the faculty are distinct from the essence of the agent. God alone is exempt from all these imperfections. He has no end proposed to Him by another; but He is Himself the last end of all things. In Him action, the power of acting, and essence are identified. He is not only living in the highest degree, He is life itself, the source and principle of all life.
ART. II. -- THE SOUL OR LIFE-PRINCIPLE OF LIVING COMPOSITES.
42. The principle of life in living composites is the soul. The soul is the first act of a physical organic body suitably disposed to receive life. -- The living composite can have life only through its substantial form. The animating form is called the soul. The soul is said to be the first act of a body, because it is the substantial form of the body, that which gives it first being and animates it. The term physical shows that the soul is proper only to natural bodies, and not to artificial and mathematical bodies. The soul is called the first act of an organic body, because the functions of the soul being different, and each of them requiring an organ of its own, every body united to a soul must necessarily have different organs. Finally, the words, suitably disposed to receive life, imply that the soul cannot be the form of every body in any condition whatever, but only of a body so disposed that it can have life and remain in the condition necessary to life. These words also convey the meaning that the property of the soul is to give life actually to the body which has only the potentiality of receiving it, and to render it capable of the operations of life, though not to constitute it always actually in operation.
43. There are three kinds of soul: vegetative, sensitive, and rational. -- There are as many kinds of soul as there are kinds of life. But as life exceeds the ordinary powers of matter, there are as many kinds of life as there are degrees in which vital operations surpass the powers of matter. These degrees are three in number. For there is (1) such action as exceeds the powers of matter in this, that it proceeds from a principle intrinsic in the subject in which it is manifested, although it is produced dependently on matter and its qualities; this is vegetative operation. For example, nutrition and the other actions related to it are produced not simply by means of corporeal organs, but also by means of the physical and chemical forces of nature. (2) There is also an operation which is exercised by means of a corporeal organ, but not in virtue of any quality proper to matter; this is sensitive operation. Thus, although moisture, heat, and other corporeal qualities are required for the operation of the senses, still the act of sensation is not produced by means of these qualities, which are requisite merely that the organ of sensation may be suitably disposed. Lastly, there is (3) an operation which surpasses corporeal nature in this, that it is not exercised in virtue of any quality proper to matter, like vegetation, nor through the concurrence of material organs, like sensation; this is the operation of the rational soul. As there are but three kinds of soul, so there are three modes of life -- the vegetative, the sensitive, and the intellectual. Locomotion, it is true, is not, strictly speaking, common to all creatures having sensitive life. A distinction may, then, be made between those animals that have only the sense of touch, and perfect animals that are made aware by their senses not only of what is near them, but also of what is far removed, that direct themselves to these distant objects, and consequently have also progressive motion. Yet all animals have at least a power of contraction and dilatation, and therefore some form of locomotion. Hence there is no need to classify locomotion as a special mode.
44. In all living composites, even in those that possess several kinds of there is only one soul that performs all the functions of life. -- In every living being, as in every composite, there is only one substantial form.{1} But experience proves that it is the soul that in the case of living composites gives first being to the body, and is, consequently, its substantial form; therefore the soul must be one. In composites having several kinds of life, there is a superior soul which performs the operations of inferior souls, just as a greater number contains the smaller numbers, or as a superior active power contains in its unity the inferior active powers. But, although one in itself, the soul of the living composite is virtually multiple and informs all the parts of the body, enabling them to exercise the various functions of life, as the same blowing (blast) in the different pipes of an organ produces various sounds, according to the dispositions of the pipes.
45. The soul is indivisible. -- The indivisibility of the soul is a truth attested by experience. For when a member of a living body is amputated, it ceases to be animated -- that is, in dividing the body, the soul has not been divided, and as the soul cannot follow the amputated member, it ceases to inform that part of the body, which is thenceforth deprived of life. In a great number of plants, however, and in the imperfect animals, the soul is accidentally divisible,{3} like the form of minerals, which though not divisible in itself, is yet divisible accidentally -- that is, in virtue of the matter in which by its imperfection it is too deeply immersed. Touching such a life principle and such a form, the same remarks may be made as of the affinity and the resistance of bodies, that although inextended in themselves, they nevertheless become extended and accidentally divisible by their entire dependence on bodies for their being.
46. The soul does not act directly by itself, but through the medium of its faculties. They are distinct from its essence and may be defined as The proximate and immediate principles of the action to which they are naturally ordained. -- The essence of the soul does not operate immediately by itself, for then it would ever be actually producing all its vital actions, since essence is unchangeable. Therefore, the operations of the soul have not the essence of the soul for their immediate principle, but faculties distinct from the essence. In God alone the power, the operation, and the essence are the same.{3}
47. Vital faculties are distinguished according to their proper acts and objects. -- Whatsoever entities are essentially related to other entities have distinctions corresponding to those found among the latter; but the vital faculties are essentially related to their proper acts, and through these acts to certain objects; therefore they are specified by these acts and these objects. Thus the eyes are intended by nature for seeing; they are specified by the act of seeing, and more remotely by the objects to be seen.
48. Although the powers of the soul are multiple, the soul itself is simple. -- The powers of the soul are necessarily multiple; for the soul produces operations which are not reducible one to the other, and which, consequently, require distinct faculties. But these faculties, although multiple, do not destroy the simplicity of the soul's essence, whence they proceed; for, since they are distinct from the essence, they do not enter into it as component parts; they are not parts of its essence, but diverse powers determining the activity of the soul's essence, which of itself is undetermined. Nevertheless, these faculties, though distinct, are not independent of one another; since the soul is one, its faculties must be subordinated one to another, that this unity may not be destroyed.{4}
49. The powers of the soul are by their nature inclined to their proper operations. -- As each power has been given to the soul for the accomplishment of a special order of actions, it must naturally be inclined to perform these actions. This natural inclination of the power does not refer to this or that individual action, but to the whole species of actions which the power can produce. Since the action is the effect of the power inclined to produce it, it is evident that the more intense the inclination of the power the more perfect will the action be. But this peculiar intensity in the inclination of one power impairs the exercise of another power. For example, he who exercises his imagination to excess will do injury to his power of judgment. This is easily explained, because the activity of the faculties is a participation of the activity of the soul. But since the soul is one and indivisible and of limited power, the concentration of its activity with particular intensity on one faculty must be prejudicial to the other faculties.
50. There are five different faculties in the soul: vegetative, sensitive, intellectual, appetitive, and locomotive. -- The faculties of the soul are divided according to their formal objects and actions. Now some powers have for their object only the body to which the soul is united; these are vegetative powers. The soul of the plant, for instance, acts only on its material organism. Other powers have for objects not only the body to which the soul is united, but everything sensible. Finally, there are powers that have for object not only everything sensible, but all being whatsoever. When the soul has for the object of its operations other beings than its own body, it may attain to them in two ways: (1) in so far as the soul knows them and is united to them by their image or species; (2) in so far as the soul is borne toward these objects. But the soul knows sensible objects through the medium of its sensitive faculties, and universal natures by its intellectual faculties. -- There are two kinds of faculties by which the soul is united to the objects to which it tends: the sensitive appetite and the rational appetite, by which it is inclined to seek its connatural good. It has also a locomotive faculty, by which it moves the body which it informs to seek what is useful and to avoid what is hurtful.
ART. III. -- THE BODIES OF LIVING COMPOSITES.
51. Living bodies differ from others in organism, origin, development, duration, mode of conservation, and reproduction. -- Living bodies differ from non-living bodies: (1) In their material constitution, because they have organs of different conformation for the special functions to be performed, and, therefore, they receive the name of organic bodies; while non-living bodies have a substance homogeneous in all its parts, and are therefore called inorganic. An organism is essential to the living composite, because diversity of vital functions calls for diverse organs. (2) In their origin, because living bodies proceed from constant causes, to which they are at first substantially united as germs; while, on the contrary, non-living bodies are produced by the accidental intervention of causes entirely external. (3) In their development, because living bodies truly grow, developing in themselves their proper type; while non-living bodies simply increase by external accretion or the addition of parts. (4) In their duration, because living bodies have an existence limited by their very nature; while the existence of non-living bodies is indefinite, and can be destroyed only by an external cause. (5) In their mode of conservation, because living bodies repair their losses by the conversion of fresh nutriment into their own substance, and are thus renewed without losing their own individuality; while non-living bodies do not repair their losses, but remain such as they were at first until they are resolved into other substances. (6) In reproduction, because living bodies are perpetuated in their species by their own virtue; while non-living bodies are multipled only by the intervention of external causes.{5}
52. The bodies of animals differ from those of plants, first, in having a more perfect vegetative organism; secondly, in having sensation; thirdly, in having a special organism adapted to the functions of sensitive life. -- Animals perform two functions, one, called vegetative, by which, like plants, they act upon their own bodies and grow, nourish, and perpetuate themselves; the other, called sensitive, by which they perceive the objects that produce a sensible impression upon them, and determine themselves to locomotion. For the functions of the first kind, they have organs generically like those of plants, but differing in this, that they produce effects more varied and above those to which the activity of plants can attain. For the functions of the second kind animals have special organs: the nervous system as the proper instrument of sensation, and the muscular system for spontaneous motion. These organs are more or less perfect according to the species in which they are found. In man the animal organism attains a special perfection, because in him sensibility is the minister and aid of the intellect. This perfection is resplendent in the beauty of man's form, in the upright posture of his body, in the extreme delicacy of the nervous and muscular systems, and in the regularity and symmetry of all the parts of his body.
ART. IV. -- VEGETATIVE LIFE, OR THE LIFE OF PLANTS.
53. The principal functions of the vegetative life are reduced to three: Nutrition, growth, and reproduction. -- By means of its organs, a plant exercises several functions, such as absorption, circulation, secretion, florification, fructification, etc.; but all these operations are reduced to the three principal ones of nutrition, growth, and reproduction. These three operations are necessary to the plant and to every living body. The third is necessary that the body maybe produced; the second, that it may attain its natural development; and the first, that it may preserve its being.
54. It is an error to attribute the life of plants to a purely mechanical principle. -- This opinion, which reduces the vital principle to physical and chemical forces, easily leads to materialism. It is opposed to the judgment of the greatest naturalists, who prove that the vital principle is distinct from the forces of matter, whether from the impossibility of obtaining a living substance by mere chemical combinations, or from the diversity that exists between the laws governing organic bodies and those governing inorganic bodies.
55. It is an error to attribute sensation to plants. -- This error has been embraced by several philosophers, as Plato and Leibnitz, and by several naturalists, as Darwin (1809-1882) and Bichat (1771-1802). But it is evident that plants are destitute of sensation: (1) because they should then have organs of sensation. but of these we see they are deprived; and (2) because plants are rooted in the soil whence they spring, and therefore sensation would serve no purpose.
ART. V. -- SENSITIVE LIFE, OR THE LIFE OF ANIMALS.
56. Every animal has the faculty of sensation and of spontaneous locomotion. -- Besides vegetative life, every animal possesses sensation and motion. But this motion is not only a change of place, produced by an intrinsic principle, of which the plant is destitute, but it is spontaneous; it is not determined by nature, but proceeds from a previous perception, and is determined by an instinctive appetition of the subject that moves. Hence, unlike motion proceeding from nature only, spontaneous motion is varied, multiple, without fixed rule, and is modified according to the different perceptions and appetitions of the animal. Spontaneous motion is seen in every animal; in the imperfect animals it consists in contraction and dilatation; in perfect animals it is progressive and complete. But because the faculty of locomotion is only a consequence of sensation, it follows that sensibility alone suffices to specify the animal.
57. The faculties of the animal are sensitive, appetitive, and locomotive. The sensitive faculties are external or internal. The external senses are five: sight, hearing, smell, taste, and toach. The internal senses are four: common sense, imagination, the estimative faculty, and memory. Appetite is concupiscible or irascible. -- External sensible bodies act on the animal. It is then necessary, first, that these bodies be united to it by the act of cognition, which takes place through the sensitive faculties both external and internal. For the animal at first knows sensible objects through one or more of the five external senses; the sensible species or representations are transmitted to the internal sense called common sense, and then to the imagination, which preserves them; the estimative faculty perceives what is useful or hurtful in the object, and its perceptions arc retained by the sensitive memory. According to its knowledge of the object as useful or as hurtful, is the animal inclined by the concupiscible appetite to seek it or shun it. If difficulties arise in seeking or shunning it, the irascible appetite strives to overcome them. Incited by the appetite, the locomotive faculty enters into action, and, in one way or another, the animal moves. All these faculties are found in a state of perfection and completeness in perfect animals. In the imperfect animals, which have no external sense but that of touch, locomotion is very imperfect, because motion, being the consequence of sensation, is more or less developed according to the development of sensation itself. In man the sensitive faculties are found in admirable harmony and with a special perfection which they receive from the intellect. Hence it is in man that these faculties should be more particularly studied; and so much the more as they cannot be well known by him, but so far forth as he experiences them himself.
58. The faculties of the brute animal are organic, that is, belonging to the composite and not to the soul only. -- Several modern philosophers, following in the footprints of Plato, consider sensation as an act of the soul only, to which the body concurs only occasionally. But this error would liken the brute soul to that of man. For if sensation has no need of organs for its production, it is a spiritual act, and the sensitive soul is spiritual, which is absurd. Besides, the diversity of the organs answering to the diverse sensitive faculties, and the necessity of these organs and their modifications for their respective sensations, prove sufficiently that these faculties belong to the composite and not to the soul alone.
59. The principle of sensitive life in the brute animal is identical with the principle of vegetative life. -- 1. Although sensitive life and vegetative life really differ from each other, and though in the body of the animal there are parts that do not possess both kinds of life, yet it is one soul that causes the functions of both in the organism which it informs. For, although the animal grows and perceives through the senses, it constitutes but one living being. Hence the formal principle from which its being and its life proceed must be one and identical. It is true that this formal principle should have the power of communicating, according to difference of disposition and aptitude in the parts of the organism, either vegetative faculties alone or both vegetative and sensitive faculties; but if it were not one and identical, it could never constitute a subject one and identical. Now, nothing is more evident than the unity and identity of every animal. 2. This identity of the principle of the two kinds of life in the animal is confirmed by the fact of the cessation of vegetative life in an organism which has become incapable of sensitive life, and vice versa. It is further confirmed by the admirable harmony that exists between the vegetative and the sensitive organs, a harmony which makes of them but one organic system, although varied in its different parts according to the different functions that it exercises, and which explains the intimate correspondence of the two kinds of life and the reciprocal influence which they exert. 3. The identity of the sensitive and the vegetative principle in the animal is also proved by the elevation which the sensitive principle gives to the functions of the vegetative life. For, although they are of the same genus in the plant and the animal, they are more perfect in the animal.
60. The brute soul, though simple and immaterial, is not immortal. -- The indivisibility and immateriality of the sensitive soul are proved (1) not only from experience, (2) but also by the unity of the brute's being, which can proceed only from a principle itself one; (3) from the nature of sensation, which perceives the whole object by a single act; (4) from the remembrance which the sentient subject keeps of the different and often contrary modifications which it has experienced, and which could not be explained if the principle were not immaterial. But the immateriality of the brute soul by no means implies its spirituality and immortality. For spirituality and immortality suppose a soul subsisting and operating by itself, independently of any material organ. But the being and operation of the animal are neither of the soul alone nor of the body alone, but of the whole composite. Therefore the soul of the animal does not operate without the body, and perishes with the body. But since it is simple, it does not perish by decomposition, nor does God annihilate it, for He annihilates none of His works. The soul of the animal perishes in some sort indirectly, forasmuch as the subject is wanting without which it cannot exist. Moreover, it is thus that all forms perish, that all forces and all the modifications of inorganic bodies and of plants perish.
61. Brutes are not automata, as Descartes maintained. -- This doctrine leads to materialism, for if a mechanism more or less perfectly constructed can produce in the animal the marvellous acts of sensation, a few additional degrees of perfection of mechanism could produce the marvellous acts of intelligence. It is in vain to urge in support of this doctrine that, if any immaterial soul be attributed to animals, we must thereby acknowledge in them a spiritual and immortal soul. The immateriality of a soul includes neither its spirituality nor its immortality. It is equally vain to invoke certain analogies with the motions of certain bodies like the magnet, or to have recourse to divine intervention to explain the operations of the animal. These motions of bodies bear no resemblance to the spontaneous motions of animals, and to have recourse to the intervention of God is to accept all the pantheistic consequences of the system of occasional causes.
62. Epicurus and all other materialists err in ascribing reason and intelligence to brutes. -- This system, which makes a man of the brute only to make a brute of man, is contrary to experience and the unanimous belief of the human race. It puts forward two arguments in its favor (1) that brutes perform their acts in a suitable manner, as man does; (2) that externally they resemble man both in their organs and in most of their actions. But these are pure sophisms. From the fact that brutes are like man in something, it does not follow that they are like him in all respects. If brutes know, they do not understand; if they form images, they do not attain to ideas; if they distinguish what is suitable to them from what is not suitable, they are yet incapable of any moral notion. Finally, if they are guided by natural instinct with admirable rectitude, it is certain that they can neither invent nor perfect anything.{6}
{1} What gives being to an entity also gives it unity; but the substantial form gives being to bodily snbstance therefore, if the substantial form were not one, the body would not be one.
{2} In these plants and animals the specific functions are few and the organism is simple and diffused; "but with a complex and multifarious organism the case is very different. It takes but little to supply the acranial head and the tail of a worm, but it would require a far more elaborate process to develop the eyes, ears, nose, a vertebrate structure, heart, lungs, etc., out of the hoof of an ox. -- Metaphysics of the School, vol. ii., p. 654, and prop. 214.
{3} See Metaphysics of the School, vol. iii., pp. 205-219, and more particularly, pp. 214-217.
{4} That there is a real distinction between the essence and the powers of the soul is manifest from our mode of speaking of them, from the very nature of the powers and their actions, and from the testimony of consciousness.
{5} Since living bodies differ essentially from non-living bodies, spontaneous generation in the sense of the production of life from no pre-existing germs and by the sole agency of physical and chemical forces is an utter impossibility. Traces of this theory are found in ancient Greek philosophy, and, in a modified form, in many of the Schoolmen, among whom are St. Bonaventure and apparently St. Thomas; but the latter merely believed that God the Creator had given to matter the power, on the presence of certain conditions, of producing the lowest and simplest forms of life, like infusoria. But the apparatus at the disposition of modern science and the persevering experiments of Flourens, Dumas, Quatrefages, and especially Pasteur, have proved that when air and water, in which the germs are disseminated, have been excluded no generation occurs. Of the result of Pasteurs experiment Tyndall says, "There is no conclusion in experimental science more certain than that." The obstinate persistency of Tiedemans, Brenser, Poncet, and Broca, in asserting the truth of spontaneous generation, has only served to bring out its falsity more clearly.
{6} The question is not whether the acts of brutes could not proceed from a rational principle, but whether they cannot and should not be traced to a sensitive principle. The instances of wonderful industry and constructive skill to be found in the animal kingdom are not to be compared with similar habits and works of man, for the brute acts by instinct, and acquires no experience, properly so called, and shows no increased perfection in process of time. Father Harper cites three classes of facts to disprove the conclusion that the brute has the same faculties as man, "only under a rudimentary form:" "1, The judgment of brutes as to what is or is not conducive to their good is not free for on the apprehension of what is useful or harmful their impulse is the result of natural operation; 2, Uniformity of operation observable in animals of the same species 3, Brute animals at the beginning of their life receive a natural estimation in order to know that which is hurtful and that which is useful, because they cannot attain to this by their own investigation; but man is left to form his judgments gradually by the practical experience of life." -- Metaphysics of the School, vol. ii., pp. 666-672.
Its importance today justifies the quotation of the following: "It is not possible to discover a link between man and the brute in any supposed order of men possessing a specific nature half-way between spirit and matter; for such a hypothesis is a contradiction in terms. A spirit cannot be more or less spirit after the manner that matter can be more or less organized. A form must be wholly spiritual or wholly unspiritual; though its faculties may be partly the one, partly the other. Neither is it possible, for the same reason, that there should be a common ancestry." -- Ibid., p. 551.