All the faculties of Vital Principle which have been enumerated belong, as we have said, to some creatures, some only of them belong to others, and there are creatures again which have but one; and we spoke of those faculties as the nutritive, appetitive, sentient, locomotive and cogitative. Of these, the nutritive alone belongs to plants; but to other beings both it and the sentient have been imparted; and if the sentient, then the appetitive, for appetite is desire, passion and volition; and all animals, without exception, have the sense of Touch. But the creature to which sensibility has been imparted cannot but be sensible of pleasure and pain, of what is grateful and what painful; and if sensible of these, it must have desire, as desire is the appetite for what is grateful. All such creatures, moreover, have the sense for food, as they have Touch, which is that sense; for all animals are nourished by what is dry and moist, warm and cold, and Touch is the sense for judging of these qualities. But it is only by chance that the Touch can judge of other qualities, as neither sound, colour nor odour contribute in aught to nourishment; and savour is among tangible qualities. Hunger and thirst are desires: the former for what is dry and warm, the latter for what is liquid and cold ; and savour is the condiment, as it were, for both. As, however, we shall be more explicit upon those points hereafter, it may, for the present, suffice to say, that all such creatures as have the sense of Touch have appetite ; it is uncertain whether or not they have imagination, but this also shall be considered hereafter. There are creatures to which, besides those faculties, locomotion has been imparted; and others again, as man, to which have been allotted both reflexion and mind, together with any other and yet nobler faculty, if such there be, than mind.
It is clear, then, that there can be but one definition for Vital Principle, as there is but one for a geometrical figure; for as in geometry there is no figure but the triangle and its sequences, so neither are there any kinds of Vital Principle save those which have been enumerated. Could there, however, be any such common expression for figures, as without being peculiar to any one, should yet be applicable to all, so might there be for the Vital Principles alluded to. It would be idle, however, to seek for any such expression, in the case either of Vital Principles or geometrical figures, as should neither be applicable to any one of them individually, nor, putting aside individuals, be applicable to them as an individual species. But still there is an analogy between the faculties of Vital Principle and geometrical figures; for as in vital properties, so in geometrical figures, the antecedent is ever present potentially in the sequences, and as the triangle is in the square, so the nutritive is in the sentient faculty. Thus, the inquiry must be conducted with reference to individuals, in order to learn what is the Vital Principle of each, as of a plant, a man, or a brute; and wherefore beings are thus ranged in a series.
Without the nutritive function there can be no sensibility, but in plants the nutritive exists without the sentient; so again without the Touch there can be no other sense, while Touch can exist alone, for many animals have neither sight nor hearing, and are altogether without smell. Among sentient creatures some have and some have not locomotion, and, finally, to a few calculation and judgment have been imparted; and to such among mortal beings as are so endowed all other faculties have been imparted likewise. But to such as possess some one only of the faculties, calculation has not been allotted, as some of them have not even imagination, while others live by it alone; it would be foreign to our present inquiry to enter upon the speculative intellect.
It is, then, clear that the definition which comes closest to each one of those faculties is also the fittest for the elucidation of Vital Principle.
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Note 1, p. 71. And all animals, without exception, have the sense of Touch, &c.] Aristotle, having observed that plants have only the function of nutrition, that is, are not sentient, proceeds to the first and, therefore, most universal of the senses—that which may, as he assumed, be present without any other, although there can be no other without it. Thus, the Touch, as perceptive of food, was supposed to be subservient to the appetite, and the Taste, as discriminating, by tangible qualities, what in food may be genial or otherwise, was held to be a modification of the Touch; but the Touch alone was by Aristotle regarded as distinctive of animal in contrast with vegetable existence. "According to the argument[1], he adds, by which appetite is said to be the mediate cause of motion, there must, in living animal bodies, be some such medium; and the being, therefore, which by its nature is incapable of motion, is impressionable by appetite, through some other faculty." Plants, that is, are not affected by the appetitive stimulus as are animals.
Note 2, p. 72. As, however, we shall be more explicit, &c.] The Touch being the earliest, so to say, of the senses and distinctive of animal existence, is here held to be the cause of appetite, as appetite is of motion; and as has been observed, the Touch was supposed to exist independently of the other senses. This sense is said to be especially discriminative of food, as animals are nourished by substances which are hot and cold, dry and moist, and these qualities are subject to it; but it can distinguish only by chance such other properties (odour, colour, sound, for instance) as do not contribute to nutrition. It is not easy to attach a definite notion to the imagination here alluded to, but as Aristotle has elsewhere distinguished the rational from the sentient imagination, and as instinct only can be assigned to creatures with one sense, it may be assumed that this is its meaning.
Note 3, p. 72. It is clear, then, that there can be but one, &c.] The triangle[2] forms all rectilineal figures, which have more than three sides, that is, "all such figures may be divided into triangles, as the square into two, the pentagon into three, the hexagon into four, &c.; and geometry has, since that age, reduced this to a special theorem."
Note 4, p. 73. Thus, the inquiry must, &c.] The conclusion here arrived at enforces the necessity of attention to individual existences, in order to ascertain what may be the distinction, if such there be, between Vital Principles; so that the question reverts to former speculations, whether or not there is but one Principle variously imparted, or whether rather, each genus of being has its own special cause of vitality and motion. It belongs, also, perhaps, to the same speculation, to ascertain why beings have been ranged in a series—why, that is, such manifold gradations of existence from man down to the zoophyte; unless, indeed, with other conditions of similar character, it is beyond the pale of human inquiry.
Note 5, p. 73. But to such as possess some one only of the faculties, &c.] It is far from easy to fix upon the exact equivalents of the original terms (λογισμὸς, διάνοια, φαντασία,) which have been here rendered by calculation, judgment and imagination; but the speculative intellect, (θεορητικὸς νοῦς) implies it may "be assumed" the human mind or understanding, which was said to be impassive, homogeneous, and distinct from all else. It might well, therefore, be regarded as foreign to an inquiry, the purport of which is to detect the animating principle of bodies fitted for receiving its influences. It is somewhat strange that Aristotle, whose teaching was so didactic, should nowhere have given a definition of that principle or being, to which he has assigned so exalted a destiny.