by Aristotle
7 · But how is it that thought is sometimes followed by action, sometimes not; sometimes by movement, sometimes not? What happens seems parallel to the case of thinking and inferring about the immovable objects. There the end is the truth seen (for, when one thinks the two propositions, one thinks and puts together [10] the conclusion), but here the two propositions result in a conclusion which is an action—for example, whenever one thinks that every man ought to walk, and that one is a man oneself, straightaway one walks; or that, in this case, no man should walk, one is a man: straightaway one remains at rest. And one so acts in the two [15] cases provided that there is nothing to compel or to prevent. Again, I ought to create a good, a house is good: straightaway he makes a house. I need a covering, a coat is a covering: I need a coat. What I need I ought to make, I need a coat: I make a coat. [20] And the conclusion ‘I must make a coat’ is an action. And the action goes back to a starting-point. If there is to be a coat, there must first be this, and if this then this—and straightaway he does this. Now that the action is the conclusion is clear. But the premisses of action are of two kinds, of the good and of the possible.
[25] And as sometimes happens in dialectical questioning, so here the intellect does not stop and consider at all the one proposition, the obvious one; for example if walking is good for man, one does not dwell upon the proposition ‘I am a man’. And so what we do without reflection, we do quickly. For when a man is actually using [30] perception or imagination or thought in relation to that for the sake of which, what he desires he does at once. For the actualizing of desire is a substitute for inquiry or thinking. I want to drink, says appetite; this is drink, says sense or imagination or thought: straightaway I drink. In this way living creatures are impelled to move and [35] to act, and desire is the last cause of movement, and desire arises through perception or through imagination and thought. And things that desire to act make and act [701a] sometimes from appetite or impulse and sometimes from wish.
The movements of animals may be compared with those of automatic puppets, which are set going on the occasion of a tiny movement (the strings are released, and the pegs strike against one another); or with the toy wagon (for the child mounts on it and moves it straight forward, and yet it is moved in a circle owing to [5] its wheels being of unequal diameter—the smaller acts like a centre on the same principle as the cylinders). Animals have parts of a similar kind, their organs, the sinewy tendons to wit and the bones; the bones are like the pegs and the iron; the tendons are like the strings; for when these are slackened or released movement [10] begins. However, in the puppets and the toy wagon there is no change of quality, since if the inner wheels became smaller and greater by turns there would be the same circular movement set up. In an animal the same part has the power of becoming now larger and now smaller, and changing its form, as the parts increase [15] by warmth and again contract by cold and change their quality. This change of quality is caused by imaginations and sensations and by ideas. Sensations are obviously a form of change of quality, and imagination and thinking have the same [20] power as the objects. For in a measure the form conceived be it of hot or cold5 or pleasant or fearful is like what the actual objects would be, and so we shudder and are frightened merely by thinking. Now all these affections are actually changes of quality, and with those changes some parts of the body enlarge, others grow smaller. [25] And it is not hard to see that a small change occurring at the centre makes great and numerous changes at the circumference, just as by shifting the rudder a hair’s breadth you get a wide deviation at the prow. And further, when by reason of heat or cold or some kindred affection a change is set up in the region of the heart, even in [30] an imperceptibly small part of the heart, it produces a vast difference in the body—blushing, let us say, or turning white, and tremblings and shivers and their opposites.
8 · But to return, the object we pursue or avoid in the field of action is, as has been explained, the origin of movement, and upon the thought and imagination of [35] this there necessarily follows a heating or chilling. For what is painful we avoid, what is pleasing we pursue, and anything painful or pleasing is generally speaking [702a1] accompanied by a chilling and heating (but we do not notice this when it happens in a small part). One may see this by considering the affections. Blind courage and panic fears, erotic motions, and the rest of the corporeal affections, pleasant and painful, are all accompanied by heating or chilling, some in a particular member, others in the body generally. So, memories and anticipations, using things of this [5] kind as likenesses, are now more and now less causes of the same changes of temperature. And so we see the reason of nature’s handiwork in the inward parts, and in the centres of movement of the organic members; they change from solid to moist, and from moist to solid, from soft to hard and vice versa. And so when these [10] are affected in this way, and when besides the passive and active have the constitution we have many times described, as often as it comes to pass that one is active and the other passive, and neither of them falls short of the elements of its account, straightaway one acts and the other responds. And on this account [15] thinking that one ought to go and going are virtually simultaneous, unless there be something else to hinder action. The organic parts are suitably prepared by the affections, these again by desire, and desire by imagination. Imagination in its turn depends either upon thinking or upon sense-perception. And the simultaneity and [20] speed are due to the natural correspondence of the active and passive.
However, that which first moves the animal organism must be in a definite origin. Now we have said that a joint is the origin of one part of a limb, the end of another. And so nature employs it sometimes as one, sometimes as two. When movement arises from a joint, one of the extreme points must remain at rest, and the [25] other be moved (for as we explained above the mover must support itself against a point at rest); accordingly, in the case of the elbow-joint, the last point of the forearm is moved but does not move anything, while, in the flexion, one point of the elbow, which lies in the whole forearm that is being moved, is moved, but there must also be a point which is unmoved, and this is our meaning when we speak of a point [30] which is in potency one, but which becomes two in actual exercise. Now if the forearm were the living animal, somewhere in its elbow-joint would be the movement-imparting origin of the soul.
Since, however, it is possible for a lifeless thing to be so related to the hand as the forearm is to the upper (for example, when a man moves a stick in his hand), it is evident that the soul could not lie in either of the two extreme points, neither, that is, [35] in the last point of what is moved, nor in the other origin. For the stick too has an end point and an origin by reference to the hand. Accordingly, for this reason, if the [702b1] moving origin which derives from the soul is not in the stick, then it is not in the hand either; for a precisely similar relation obtains between the extremity of the hand and the wrist, and between the wrist and the elbow. In this matter it makes no difference whether the part is naturally connected to the body or not; the stick may [5] be looked at as a detached part-of the whole. It follows then of necessity that it cannot lie in any origin which is the end of another member, even though there may lie another part outside the one in question. For example, relatively to the end point of the stick the hand is the origin, but the origin of the hand’s movement is in the [10] wrist. And so if it is not even in the hand, because there is still something higher up, neither is the origin here; for once more if the elbow is at rest the whole part below it can be moved as a continuous whole.
9 · Now since the left and the right sides are symmetrical, and these opposites are moved simultaneously, it cannot be that the left is moved by the right [15] remaining stationary, nor vice versa; the origin must always be in what lies above both. Therefore, the origin of the moving soul must be in the middle; for of both extremes the middle is the limiting point; and this is similarly related to the movements from above and below—e.g. from the head—and to those which spring from th
e spinal column, in creatures that have a spinal column.
[20] And this is a reasonable arrangement. For the sensorium is in our opinion in the centre too; and so, if the region of the origin is altered through sense-perception and thus changes, the adjacent parts change with it and they too are extended or contracted, and in this way the movement of the creature necessarily follows. And [25] the middle of the body must needs be in potency one but in actuality more than one; for the limbs are moved simultaneously from the origin, and when one is at rest the other is moved. For example, in the line ABC, B is moved, and A is the mover. There [30] must, however, be a point at rest if one is to move, the other to be moved. A then being one in potency must be two in actuality, and so be a magnitude not a point. Again, C may be moved simultaneously with B. Both the origin then in A must move and be moved, and so there must be something other than them which moves [35] but is not moved. For otherwise, when the movement begins, the extremes, i.e. the origin, in A would rest upon one another, like two men putting themselves back to [703a1] back and so moving their legs. There must then be some one thing which moves both. This something is the soul, distinct from the magnitude just described and yet located therein.
10 · Although from the point of view of the account which gives the cause of [5] movement desire is the middle, and desire moves being moved, still in the animated body there must be some body of this kind. Now that which is moved, but whose nature is not to initiate movement, is capable of being passive to an external power, while that which initiates movement must needs possess a kind of force and power. Now it is clear that animals do both possess connatural spirit and derive force from [10] this. (How this connatural spirit is maintained in the body is explained in other passages of our works.) And this spirit appears to stand to the soul-origin in a relation analogous to that between the point in a joint which moves being moved and the unmoved. Now since this origin is for some animals in the heart, in the rest in a [15] part analogous with the heart, for this reason the connatural spirit is clearly there too. (The question whether the spirit remains always the same or constantly changes must be discussed elsewhere; for the same question arises about the rest of the parts of the body.) At all events we see that it is well disposed to excite movement and to exert force. Now the functions of movement are thrusting and pulling. Accordingly, the organ of movement must be capable of expanding and [20] contracting; and this is precisely the characteristic of spirit. It contracts and expands without constraint, and so is able to pull and to thrust from one and the same cause, exhibiting weight compared with the fiery element, and lightness by comparison with the opposites of fire. Now that which is to initiate movement [25] without alteration must be of the kind described; for the natural bodies prevail over one another by dint of predominance; the light is overcome and kept down by the heavier, and the heavy kept up by the lighter.
We have now explained what the part is which is moved when the soul originates movement, and what is the reason for this. And the animal organism must be conceived after the similitude of a well-governed commonwealth. When [30] order is once established in a city there is no more need of a separate monarch to preside over each several task. The individuals each play their assigned part as it is ordered, and one thing follows another because of habit. So in animals the same thing happens because of nature, each part naturally doing its own work as nature [35] has composed it. There is no need then of a soul in each part, but it resides in a kind of origin of the body, and the remaining parts live by being naturally connected, and [703b1] play their parts because of their nature.
11 · So much then for the voluntary movements of animal bodies, and the reasons for them. These bodies, however, display in certain members involuntary [5] movements too, but most often non-voluntary movements. By involuntary I mean motions of the heart and of the penis; for often upon an image arising and without express mandate of the intellect these parts are moved. By non-voluntary I mean sleep and waking and respiration, and other similar movements. For neither imagination nor desire is properly mistress of any of these. But since the animal [10] body must undergo natural changes of quality, and when the parts are so altered some must increase and others decrease, so that the body must straightaway be moved and change with the changes that nature makes dependent upon one another (the causes of the movements are heatings and chillings, both those coming from [15] outside the body, and those taking place naturally within it)—so the movements which occur in spite of reason in the aforesaid parts occur when a change of quality supervenes. For thinking and imagination, as we said above, produce that which brings about the affections, since they produce the forms which bring them about. [20] And the parts aforesaid display this motion more conspicuously than the rest, because each is in a sense a separate animal, the reason being that each contains vital moisture.6 In the case of the heart the cause is plain; for it contains the origins of the senses; while an indication that the generative organ too is vital is that there [25] flows from it the seminal potency, itself a kind of living creature. Again, it is a reasonable arrangement that the movements arise in the origin upon movements in the parts, and in the parts upon movements in the origin, and so reach one another. [30] Conceive A to be the origin. The movements then arrive at the origin from each letter in the diagram we have drawn, and back again from the origin which is moved and changes, (for it is potentially multiple) the movement of B goes to B, that of C to C, the movement of both to both; but from B to C the movements flow by dint of [35] going from B to A as to an origin, and then from A to C as from an origin. And a movement contrary to reason sometimes does and sometimes does not arise in the parts on the occasion of the same thoughts; the reason is that sometimes the matter [704a1] which is passive is there in sufficient quantity and of the right quality and sometimes not.
And so we have finished our account of the reasons for the parts of each kind of [704b1] animal, of the soul, and further of sense-perception, of sleep, of memory, and of movement in general; it remains to speak of generation.
**TEXT: M. C. Nussbaum, Aristotle’s de Motu Animalium, Princeton University Press, Princeton, N.J., 1978
1See Physics VIII; On the Heavens I.
2See Iliad VIII 20–22.
3See On the Soul I 3–4.
4See Metaphysics Λ 7.
5Nussbaum excises θερμoῦ ἢ ψυχρoῦ ἤ.
6Nussbaum, following Jaeger, excises τoύτoυ … ζωτικήν.
PROGRESSION OF ANIMALS**
A.S. L. Farquharson
1 · We have now to consider the parts which are useful to animals for [704a5] movement in place; first, why each part is such as it is and to what end they possess them; and second, the differences between these parts both in one and the same creature, and again by comparison of the parts of creatures of different species with one another. First then let us lay down how many questions we have to consider.
The first is what are the fewest points of motion necessary to animal [10] progression, the second why sanguineous animals have four points and not more, but bloodless animals more than four, and generally why some animals are footless, others bipeds, others quadrupeds, others polypods, and why all have an even number of feet, if they have feet at all; why the points on which progression depends [15] are even in number.
Next, why are man and bird bipeds, but fish footless; and why do man and bird, though both bipeds, have an opposite curvature of the legs. For man bends his legs convexly, a bird has his bent concavely; again, man bends his arms and legs in [20] opposite directions, for he has his arms bent convexly, but his legs concavely. and a viviparous quadruped bends his limbs in opposite directions to a man’s, and in opposite directions to one another; for he has his forelegs bent convexly, his hind [704b5] legs concavely. Again, quadrupeds which are not viviparous but oviparous have a peculiar curvature of the limbs laterally away from the body. Again, why do quadrupeds move their legs criss cross?
We have to examine the reasons for all the
se facts, and others cognate to them; that the facts are such is clear from our natural history, we have now to ask reasons [10] for the facts.
2 · At the beginning of the inquiry we must postulate the principles we are accustomed constantly to use for our scientific investigation of nature, that is we must take for granted principles of this universal character which appear in all nature’s work. Of these one is that nature creates nothing without a purpose, but [15] always the best possible in each kind of living creature by reference to its essential constitution. Accordingly if one way is better than another that is the way of nature. Next we must take for granted the different species of dimensions which inhere in [20] various things; of these there are three pairs of two each, superior and inferior, before and behind, to the right and to the left. Further we must assume that the sources of movements in place are thrusts and pulls. (These are the essential [705a1] place-movements, it is only accidentally that what is carried by another is moved; it is not thought to move itself, but to be moved by something else.)