Two things are to be remembered respecting Matter, in its Aristotelian (logical or ontological) sense: (1) It may be Body, but it is not necessarily Body;39 (2) It is only intelligible as the correlate of Form: it can neither exist by itself, nor can it be known by itself (i.e., when taken out of that relativity). This deserves notice, because to forget the relativity of a relative word, and to reason upon it as if it were an absolute, is an oversight not unfrequent. Furthermore, each variety of Matter has its appropriate Form, and each variety of Form its appropriate Matter, with which it correlates. There are various stages or gradations of Matter; from Materia Prima, which has no Form at all, passing upwards through successive partial developments to Materia Ultima; which last is hardly40 distinguishable from Form or from Materia Formata.

The distinction above specified is employed by Aristotle in his exposition of the Soul. The soul belongs to the Category of Substance or Essence (not to that of Quantity, Quality, &c.); but of the two points of view under which Essence may be presented, the soul ranks with Form, not with Matter — with the Actual, not with the Potential. The Matter to which (as correlate) soul stands related, is a natural body (i.e., a body having within it an inherent principle of motion and rest) organized in a certain way, or fitted out with certain capacities and preparations to which soul is the active and indispensable complement. These capacities would never come into actuality without the soul; but, on the other hand, the range of actualities or functions in the soul depends upon, and is limited by, the range of capacities ready prepared for it in the body. The implication of the two constitutes the living subject, with all its functions, active and passive. If the eye were an animated or living subject, seeing would be its soul; if the carpenter’s axe were living, cutting would be its soul;41 the matter would be the lens or the iron in which this soul is embodied. It is not indispensable, however, that all the functions of the living subject should be at all times in complete exercise: the subject is still living, even while asleep; the eye is still a good eye, though at the moment closed. It is enough if the functional aptitude exist as a dormant property, ready to rise into activity, when the proper occasions present themselves. This minimum of Form suffices to give living efficacy to the potentialities of body; it is enough that a man, though now in a dark night and seeing nothing, will see as soon as the sun rises; or that he knows geometry, though he is not now thinking of a geometrical problem. This dormant possession is what Aristotle calls the First Entelechy or Energy, i.e., the lowest stage of Actuality, or the minimum of influence required to transform Potentiality into Actuality. The Aristotelian definition of Soul is thus: The first entelechy of a natural organized body, having life in potentiality.42 This is all that is essential to the soul; the second or higher entelechy (actual exercise of the faculties) is not a constant or universal property.43

In this definition of Soul, Aristotle employs his own Philosophia Prima to escape the errors committed by prior philosophers. He does not admit that the soul is a separate entity in itself; or that it is composed (as Empedokles and Demokritus had said) of corporeal elements, or (as Plato had said) of elements partly corporeal, partly logical and notional. He rejects the imaginary virtues of number, invoked by the Pythagoreans and Xenokrates; lastly, he keeps before him not merely man, but all the varieties of animated objects, to which his definition must be adapted. His first capital point is to put aside the alleged identity, or similarity, or sameness of elements, between soul and body; and to put aside equally any separate existence or substantiality of soul. He effects both these purposes by defining them as essentially relatum and correlate; the soul, as the relatum, is unintelligible and unmeaning without its correlate, upon which accordingly its definition is declared to be founded.

The real animated subject may be looked at either from the point of view of the relatum or from that of the correlate; but, though the two are thus logically separable, in fact and reality they are inseparably implicated; and, if either of them be withdrawn, the animated subject disappears. “The soul (says Aristotle) is not any variety of body, but it cannot be without a body; it is not a body, but it is something belonging to or related to a body; and for this reason it is in a body, and in a body of such or such potentialities.”44 Soul is to body (we thus read), not as a compound of like elements, nor as a type is to its copy, or vice versâ, but as a relatum to its correlate; dependent upon the body for all its acts and manifestations, and bringing to consummation what in the body exists as potentiality only. Soul, however, is better than body; and the animated being is better than the inanimate by reason of its soul.45

The animated subject is thus a form immersed or implicated in matter; and all its actions and passions are so likewise.46 Each of these has its formal side, as concerns the soul, and its material side, as concerns the body. When a man or animal is angry, for example, this emotion is both a fact of the soul and a fact of the body: in the first of these two characters, it may be defined as an appetite for hurting some one who has hurt us; in the second of the two, it may be defined as an ebullition of the blood and heat round the heart.47 The emotion, belonging to the animated subject or aggregate of soul and body, is a complex fact having two aspects, logically distinguishable from each other, but each correlating and implying the other. This is true not only in regard to our passions, emotions, and appetites, but also in regard to our perceptions, phantasms, reminiscences, reasonings, efforts of attention in learning, &c. We do not say that the soul weaves or builds (Aristotle observes48): we say that the animated subject, the aggregate of soul and body, the man, weaves or builds. So we ought also to say, not that the soul feels anger, pity, love, hatred, &c., or that the soul learns, reasons, recollects, &c., but that the man with his soul does these things. The actual movement throughout these processes is not in the soul, but in the body; sometimes going to the soul (as in sensible perception), sometimes proceeding from the soul to the body (as in the case of reminiscence). All these processes are at once corporeal and psychical, pervading the whole animated subject, and having two aspects coincident and inter-dependent, though logically distinguishable. The perfect or imperfect discrimination by the sentient soul depends upon the good or bad condition of the bodily sentient organs; an old man that has become shortsighted would see as well as before, if he could regain his youthful eye. The defects of the soul arise from defects in the bodily organism to which it belongs, as in cases of drunkenness or sickness; and this is not less true of the Noûs, or intellective soul, than of the sentient soul.49 Intelligence, as well as emotion, are phenomena, not of the bodily organism simply, nor of the Noûs simply, but of the community or partnership of which both are members; and, when intelligence gives way, this is not because the Noûs itself is impaired, but because the partnership is ruined by the failure of the bodily organism.

Respecting the Noûs (the theorizing Noûs), we must here observe that Aristotle treats it as a separate kind or variety of soul, with several peculiarities. We shall collect presently all that he says upon that subject, which is the most obscure portion of his psychology.

In regard to soul generally, the relative point of view with body as the correlate is constantly insisted on by Aristotle; without such correlate his assertions would have no meaning. But the relation between them is presented in several different ways. The soul is the cause and principle of a living body;50 by which is meant, not an independent and pre-existent something that brings the body into existence but, an immanent or indwelling influence which sustains the unity and guides the functions of the organism. According to the quadruple classification of Cause recognized by Aristotle — Formal, Material, Movent, and Final — the body furnishes the Material Cause, while the soul comprises all the three others. The soul is (as we have already seen) the Form in relation to the body as Matter, but it is, besides, the Movent, inasmuch as it determines the local displacement as well as all the active functions of the body — nutrition, growth, generation, sensation, &c.; lastly, it is also the Final Cause, since the maintenance and perpetuation of the same Form, in successive individuals, is the standing purpose aimed at by each body in the economy of Nature.51 Under this diversity of aspect, soul and body are reciprocally integrant and complementary of each other, the real integer (the Living or Animated Body) including both.

Soul, in the Aristotelian point of view — what is common to all living bodies, comprises several varieties. But these varieties are not represented as forming a genus with co-ordinate species under it, in such manner that the counter-ordinate species, reciprocally excluding each other, are, when taken together, co-extensive with the whole genus; like man and brute in regard to animal. The varieties of soul are distributed into successive stages gradually narrowing in extension and enlarging in comprehension; the first or lowest stage being co-extensive with the whole, but connoting only two or three simple attributes; the second, or next above, connoting all these and more besides, but denoting only part of the individuals denoted by the first; the third connoting all this and more, but denoting yet fewer individuals; and so on forward. Thus the concrete individuals, called living bodies, include all plants as well as all animals; but the soul, called Nutritive by Aristotle, corresponding thereto connotes only nutrition, growth, decay, and generation of another similar individual.52 In the second stage, plants are left out, but all animals remain: the Sentient soul, belonging to animals, but not belonging to any plants, connotes all the functions and unities of the Nutritive soul, together with sensible perception (at least in its rudest shape) besides.53 We proceed onward in the same direction, taking in additional faculties — the Movent, Appetitive, Phantastic (Imaginative), Noëtic (Intelligent) soul, and thus diminishing the total of individuals denoted. But each higher variety of soul continues to possess all the faculties of the lower. Thus the Sentient soul cannot exist without comprehending all the faculties of the Nutritive, though the Nutritive exists (in plants) without any admixture of the Sentient. Again, the Sentient soul does not necessarily possess either memory, imagination, or intellect (Noûs); but no soul can be either Imaginative or Noëtic, without being Sentient as well as Nutritive. The Noëtic Soul, as the highest of all, retains in itself all the lower faculties; but these are found to exist apart from it.54

We may remark here that the psychological classification of Aristotle proceeds in the inverse direction to that of Plato. In the Platonic Timæus we begin with the grand soul of the Kosmos, and are conducted by successive steps of degradation to men, animals, plants; while Aristotle lays his foundation in the largest, most multiplied, and lowest range of individuals, carrying us by successive increase of conditions to the fewer and the higher.

The lowest or Nutritive soul, in spite of the small number of conditions involved in it, is the indispensable basis whereon all the others depend. None of the other souls can exist apart from it.55 It is the first constituent of the living individual — the implication of Form with Matter in a natural body suitably organized; it is the preservative of the life of the individual, with its aggregate of functions and faculties, and with the proper limits of size and shape that characterize the species;56 it is, moreover, the preservative of perpetuity to the species, inasmuch as it prompts and enables each individual to generate and leave behind a successor like himself; which is the only way that an individual can obtain quasi-immortality, though all aspire to become immortal.57 This lowest soul is the primary cause of digestion and nutrition. It is cognate with the celestial heat, which is essential also as a co-operative cause; accordingly, all animated bodies possess an inherent natural heat.58

We advance upwards now from the nutritive soul to that higher soul which is at once nutritive and Sentient; for Aristotle does not follow the example of Plato in recognizing three souls to one body, but assigns only one and the same soul, though with multiplied faculties and functions, to one and the same body. Sensible perception, with its accompaniments, forms the characteristic privilege of the animal as contrasted with the plant.59 Sensible perception admits of many diversities, from the simplest and rudest tactile sensation, which even the lowest animals cannot be without, to the full equipment of five senses which Aristotle declares to be a maximum not susceptible of increase.60 But the sentient faculty, even in its lowest stage, indicates a remarkable exaltation of the soul in its character of form. The soul, quâ sentient and percipient, receives the form of the perceptum without the matter; whereas the nutritive soul cannot disconnect the two, but receives and appropriates the nutrient substance, form and matter in one and combined.61 Aristotle illustrates this characteristic feature of sensible perception by recurring to his former example of the wax and the figure. Just as wax receives from a signet the impression engraven thereon, whether the matter of the signet be iron, gold, stone, or wood; as the impression stamped has no regard to the matter, but reproduces only the figure engraven on the signet, the wax being merely potential and undefined, until the signet comes to convert it into something actual and definite;62 so the percipient faculty in man is impressed by the substances in nature, not according to the matter of each but, according to the qualitative form of each. Such passive receptivity is the first and lowest form of sensation,63 not having any magnitude in itself, but residing in bodily organs which have magnitude, and separable from them only by logical abstraction. It is a potentiality, correlating with, and in due proportion to, the exterior percipibile, which, when acting upon it, brings it into full actuality. The actuality of both (percipiens and perceptum) is one and the same, and cannot be disjoined in fact, though the potentialities of the two are distinct yet correlative; the percipiens is not like the percipibile originally, but becomes like it by being thus actualized.64

The sentient soul is communicated by the male parent in the act of generation,65 and is complete from the moment of birth, not requiring a process of teaching after birth; the sentient subject becomes at once and instantly, in regard to sense, on a level with one that has attained a certain actuality of cognition, but is not at the moment reflecting upon the cognitum. Potentiality and Actuality are in fact distinguishable into lower and higher degrees; the Potential that has been actualized in a first or lower stage, is still a Potential relatively to higher stages of Actuality.66 The Potential may be acted upon in two opposite ways; either by deadening and extinguishing it, or by developing and carrying it forward to realization. The sentient soul, when asleep or inert, requires a cause to stimulate it into actual seeing or hearing; the noëtic or cognizant soul, under like circumstances, must also be stimulated into actual meditation on its cognitum. But there is this difference between the two. The sentient soul communes with particulars; the noëtic soul with universals. The sentient soul derives its stimulus from without, and from some of the individual objects, tangible, visible, or audible; but the noëtic soul is put into action by the abstract and universal, which is in a certain sense within the soul itself; so that a man can at any time meditate on what he pleases, but he cannot see or hear what he pleases, or anything except such visible or audible objects as are at hand.67

We have already remarked, that in many animals the sentient soul is little developed; being confined in some to the sense of touch (which can never be wanting),68 and in others to touch and taste. But even this minimum of sense — though small, if compared with the variety of senses in man — is a prodigious step in advance of plants; it comprises a certain cognition, and within its own sphere it is always critical, comparing, discriminative.69 The sentient soul possesses this discriminative faculty in common with the noëtic soul or Intelligence, though applied to different objects and purposes; and possesses such faculty, because it is itself a mean or middle term between the two sensible extremes of which it takes cognizance, — hot and cold, hard and soft, wet and dry, white and black, acute and grave, bitter and sweet, light and darkness, visible and invisible, tangible and intangible, &c. We feel no sensation at all when the object touched is exactly of the same temperature with ourselves, neither hotter nor colder; the sentient soul, being a mean between the two extremes, is stimulated to assimilate itself for the time to either of them, according as it is acted upon from without. It thus makes comparison of each with the other, and of both with its own mean.70 Lastly, the sentient faculty in the soul is really one and indivisible, though distinguishable logically or by abstraction into different genera and species.71 Of that faculty the central physical organ is the heart, which contains the congenital or animal spirit. The Aristotelian psychology is here remarkable, affirming as it does the essential relativity of all phenomena of sense to the appreciative condition of the sentient; as well as the constant implication of intellectual and discriminative comparison among them.

All the objects generating sensible perception, are magnitudes.72 Some perceptions are peculiar to one sense alone, as colour to the eye, &c. Upon these we never make mistakes directly; in other words, we always judge rightly what is the colour or what is the sound, though we are often deceived in judging what the thing coloured is, or where the sonorous object is.73 There are, however, some perceivables not peculiar to any one sense alone, but appreciable by two or more; though chiefly and best by the sense of vision; such are motion, rest, number, figure, magnitude. Here the appreciation becomes less accurate, yet it is still made directly by sense.74 But there are yet other matters that, though not directly affecting sense, are perceived indirectly, or by way of accompaniment to what is directly perceived. Thus we see a white object; nothing else affecting our sense except its whiteness. Beyond this, however, we judge and declare, that the object so seen is the son of Kleon. This is a judgment obtained indirectly, or by way of accompaniment; by accident, so to speak, inasmuch as the same does not accompany all sensations of white. It is here that we are most liable to error.75