The Politics of Aristotle

by Aristotle

  In all the changes described that which moves now extends itself in a straight [5] line to progress, and now is hooped; it straightens itself in its leading part, and is hooped in what follows behind. Even jumping animals all make a flexion in the part of the body which is underneath, and after this fashion make their leaps. So too [10] flying and swimming things progress, the one straightening and bending their wings to fly, the other their fins to swim. Of the latter some have four fins, others which are rather long, for example eels, have only two. These swim by substituting a flexion of the rest of their body for the pair of fins to complete the movement, as we [15] have said before. Flat fish use two fins, and the flat of their body as a substitute for the absent pair of fins. Quite flat fish, like the ray, produce their swimming movement with the actual fins and with the outer peripheries of their body, bending and straightening themselves alternately.

  [20] 10 · A difficulty might perhaps be raised about birds. How, it may be said, can they, either when they fly or when they walk, be said to move at four points? Now we did not say that all Sanguinea move at four points, but merely at not more than four. Moreover, they cannot as a fact fly if their legs be removed, nor walk [25] without their wings. Even a man does not walk without moving his shoulders. Everything indeed, as we have said, makes a change of place by flexion and straightening, for all things progress upon what being beneath them as it were gives way up to a point; accordingly, even if there be no flexion in another member, there [30] must be at least in the point whence motion begins, that is in sheath-winged insects and in birds at the base of the wing, in others at the base of the corresponding [710a1] member, the fins, for instance, in fishes. In others, for example snakes, the flexion begins in the joints of the body.

  In winged creatures the tail serves, like a ship’s rudder, to keep the flying thing in its course. The tail then must like other limbs be able to bend at the point of [5] attachment. And so flying insects, and birds whose tails are ill-adapted for the use in question, for example peacocks, and domestic cocks, and generally birds that hardly fly, cannot steer a straight course. Flying insects have absolutely no tail, and so drift along like a rudderless vessel, and beat against anything they happen upon; [10] and this applies equally to sharded insects, like the scarab-beetle and the chafer, and to unsharded, like bees and wasps. Further, birds that are not made for flight have a tail that is of no use; for instance the purple coot and the heron and all [15] water-fowl. These fly stretching out their feet as a substitute for a tail, and use their legs instead of a tail to direct their flight. The flight of insects is slow and frail because the character of their wings is not proportionate to the bulk of their body; this is heavy, their wings small and frail, and so the flight they use is like a cargo [20] boat attempting to make its voyage with oars; now the frailty both of the actual wings and of the outgrowths upon them contributes in a measure to the flight described. Among birds, the peacock’s tail is at one time useless because of its size, at another because it is shed. But birds are in general at the opposite pole to flying [25] insects as regards their feathers, but especially the swiftest flyers among them. (These are the birds with curved talons, for swiftness of wing is useful to their mode of life.) The rest of their bodily structure is in harmony with their swift movement, [30] the small head, the slight neck, the strong and acute breastbone (acute like the prow of a clipper-built vessel, so as to be compact, and strong by dint of its mass of flesh), in order to be able to push away the air that beats against it, and that easily and [710b1] without exhaustion. The hind-quarters, too, are light and taper again, in order to conform to the movement of the front and not by their breadth to sweep the air.

  11 · So much then for these questions. But why an animal that is to stand [5] erect must necessarily be a biped, and must also have the superior parts of the body lighter, and those that lie under these heavier, is plain. Only if situated like this could it possibly carry itself easily. And so man, the only erect animal, has legs longer and stouter relatively to the upper parts of his body than any other animal [10] with legs. What we observe in children also is evidence of this. Children cannot walk erect because they are always dwarf-like, the upper parts of their bodies being too long and too stout in proportion to the lower. With advancing years the lower [15] increase disproportionately, until they get their appropriate size, and then they succeed in walking erect. Birds are light yet stand on two legs because their weight is set back, after the principle of horses fashioned in bronze with their forelegs [20] prancing. But their being bipeds and able to stand is above all due to their having the hip-bone shaped like a thigh, and so large that it looks as if they had two thighs, one in the leg before the knee-joint, the other joining this part to the fundament. Really this is not a thigh but a hip, and if it were not so large the bird could not be a [25] biped. As in a man or a quadruped, the thigh and the rest of the leg would be attached immediately to quite a small hip; consequently the whole body would be tilted too far forward. As it is, however, the hip is long and extends right along to the middle of the belly, so that the legs are attached at that point and carry as supports the whole frame. It is also evident from these considerations that a bird cannot [30] possibly be erect in the way in which man is. For as it holds its body now the wings are naturally useful to it, but if it were erect they would be as useless as the wings of [711a1] Cupids we see in pictures. It is clear at the same time from what we said that the form of no human nor any similar being permits of wings; not only because it would, though sanguineous, be moved at more than four points, but also because to have [5] wings would be useless to it when moving naturally. And nature makes nothing contrary to nature.

  12 · We have stated above that without flexion in the legs or shoulders and [10] hips no sanguineous animal with feet could progress, and that flexion is impossible except some point be at rest, and that men and birds, both bipeds, bend their legs in opposite directions, and further that quadrupeds bend theirs in opposite directions, and in the opposite way to a man’s limbs. For men bend their arms backwards, their legs forwards; quadrupeds their forelegs forwards, their back legs backwards, and [15] in like manner also birds bend theirs. The reason is that nature’s workmanship is never purposeless, as we said above, but everything for the best possible in the circumstances. Inasmuch, therefore, as all creatures which naturally have the power of changing position by the use of limbs, must have one leg stationary with [20] the weight of the body on it, and when they move forward the leg which has the leading position must be unencumbered, and the progression continuing the weight [25] must be shifted to it again, it is evidently necessary for the leg from being bent to become straight again, while the point of movement of the leg thrust forward and its lower part remain still. And it is possible for this to take place and at the same time for the animal to go forward, if the leading leg has its articulation forwards, [30] impossible if it be backwards. For, if it be forwards the stretching out of the leg will occur while the body is going forwards, but, if the other way, while it is going backwards. And again, if the flexion were backwards, the placing of the foot would be made by two movements and those contrary to one another, one, that is, [711b1] backwards and one forwards; for in the bending together of the limb the end of the thigh would go backwards, and the shin would move the foot forwards away from [5] the flexion; whereas, with the flexion forwards, the progression described will be performed not with contrary motions, but with one forward motion.

  Now man, being a biped and making his change of position in the natural way with his two legs, bends them forward for the reasons set forth, but his arms bend [10] backwards reasonably enough. If they bent the opposite way they would be useless for the work of the hands, and for taking food. But quadrupeds which are viviparous7 necessarily bend their front legs forwards. For these lead when they move, and are also in the fore-part of their body. The reason that they bend forward [15] is the same as in the case of man, for in this respect they are like mankind. And so qu
adrupeds as well bend these legs forward in the manner described. Moreover, if the flexion is like this, they are enabled to lift their feet high; if they bent them in the [20] opposite way they would only lift them a little way from the ground, because the whole thigh and the joint from which the shin-bone springs would lie under the belly as the beast moved forward. If, however, the flexion of the hind legs were forwards the lifting of these feet would be similar to that of the forefeet (for the hind legs, too, [25] would in this case have only a little room for their lifting inasmuch as both the thigh and the knee-joint would fall under the position of the belly); but the flexion being backwards, as in fact it is, nothing comes in the way of their progression with this mode of moving the feet. Moreover, it is necessary or at least better for their legs to [30] bend thus when they are suckling their young, with a view to such ministrations. If the flexion were inwards it would be difficult to keep their young under them and to shelter them.

  [712a1] 13 · Now there are four modes of flexion if we take the combinations in pairs.8 Fore and hind may bend either both backwards, as the figures marked A, or in the opposite way both forwards, as in B, or in converse ways and not in the same [5] direction, as in C where the fore bend forwards and the hind bend backwards, or as in D, the opposite way to C, where the convexities are turned towards one another and the concavities outwards. Now no biped or quadruped bends his limbs like the [10] figures A or B, but the quadrupeds like C, and like D only the elephant among quadrupeds and man if you consider his arms as well as his legs. For he bends his arms concavely and his legs convexly.

  In man, too, the flexions of the limbs are always alternately opposite; for example the elbow bends back, but the wrist of the hand forwards, and again the [15] shoulder forwards. In like fashion, too, in the case of the legs, the hip backwards, the knee forwards, the ankle in the opposite way backwards. And plainly the lower limbs are opposed in this respect to the upper, because the first principles are opposed, the shoulder bending forwards, the hip backwards; and that is why the [20] ankle bends backwards, and the wrist of the hand forwards.

  14 · This is the way then the limbs bend, and for the reasons given. But the hind limbs move criss-cross with the fore limbs; after the right fore they move the [25] left hind, then the left fore, and then the right hind. The reason is that if they moved the forelegs together and first, the animal would be wrenched or the progression would be a stumbling forwards with the hind parts as it were dragged after. Again, [30] that would not be walking but jumping, and it is hard to make a continuous change of place, jumping all the time. Here is evidence of what I say; even as it is, all horses that move in this way soon begin to refuse, for example the horses in a religious procession. For these reasons the fore limbs and the hind limbs do not move in this [712b1] separate way. And if they moved both the right legs first the weight would be outside the supporting limbs and they would fall. If then it is necessary to move in one or other of these ways or criss-cross fashion, and neither of these two is possible, [5] they must move criss-cross; for moving in the way we have said they cannot possibly experience either of these results. And this is why horses and such-like animals stand still with their legs put forward criss-cross, not with the right or the left put forward together at once. In the same fashion animals with more than four legs [10] make their movements; if you take two consecutive pairs of legs the hind always move criss-cross with the forelegs; you can see this if you watch them moving slowly. Even crabs move in this way, and they are polypods. They, too, always move criss-cross in whichever direction they are making progress. For this animal has a [15] movement all its own; it is the only animal that moves not forwards, but obliquely. Yet since forwards is a distinction relative to the line of vision, nature has made its eyes able to conform to its limbs; for its eyes can move themselves obliquely, and therefore after a fashion crabs too in this sense move forwards. [20]

  15 · Birds bend their legs in the same way as quadrupeds. For their natural construction is broadly speaking nearly the same. That is, in birds the wings are a substitute for the forelegs; and so they are bent in the same way as the forelegs of a [25] quadruped, since when they move to progress the natural beginning of change is from the wings. Flight in fact is their appropriate movement. And so if the wings be cut off a bird can neither stand still nor go forwards.

  Again, the bird though a biped is not erect, and has the forward parts of the [30] body lighter than the hind, and so it is necessary (or at least better) for the standing posture to have the thigh so placed below the body as it actually is, I mean growing towards the back. If then it must have this situation the flexion of the leg must be backwards, as in the hind legs of quadrupeds. The reasons are the same as those [713a1] given in the case of viviparous quadrupeds.

  In general, in the case of birds and winged insects, and animals which swim in [5] a watery medium, all I mean that make their progress in water by dint of organs of movement, it is not difficult to see that it is better to have the attachment of the parts in question oblique to the frame, exactly as in fact we see it to be both in birds and insects. And this same arrangement obtains also among fishes. Among birds [10] the wings are attached obliquely; so are the fins in water animals, and the wings of insects.9 In this way they divide10 the air or water most quickly and with most force and so effect their movement. For the hinder parts in this way would follow [15] forwards as they are carried along in the yielding medium, some in the water, others in the air.

  Of oviparous quadrupeds all those that live in holes, like crocodiles, lizards, spotted lizards, freshwater tortoises, and turtles, have their legs attached obliquely [20] and stretched out over the ground, and bend them obliquely. The reason is that this is useful for ease in creeping into holes, and for sitting upon their eggs and guarding them. And as they project outwards they must of necessity tuck in their thighs and put them under them in order to achieve the lifting of the whole body. In view of this [25] they cannot bend them otherwise than outwards.

  16 · We have already stated the fact that non-sanguineous animals with limbs are polypods and none of them quadrupeds. And the reason why their legs, except the extreme pairs, are necessarily attached obliquely and have their flexions [30] upwards, and the legs themselves are somewhat bowed backwards is plain. In all such creatures the intermediate legs both lead and follow. If then they were under [713b1] them, they would have to have their flexion both forwards and backwards; on account of leading, forwards; and on account of following, backwards. Now since they have to do both, for this reason their limbs are bowed and bent obliquely, [5] except the extreme pairs. (These are more natural in their movement, the front leading and the back following.) Another reason for this kind of flexion is the number of their legs; arranged in this way they would interfere less with one another in progression and not knock together. But the reason that they are bandy is that all [10] of them or most of them live in holes; for creatures living so cannot possibly be high above the ground.

  But crabs are in nature the oddest of the polypods; they do not progress forwards except in the sense explained above, and they are the only animals which have more than one pair of leading limbs. The explanation of this is the hardness of [15] their limbs, and the fact that they use them not for swimming but for walking; they always keep on the ground. However, the flexion of the limbs of all polypods is oblique, like that of the quadrupeds which live in holes—for example lizards and [20] crocodiles and many of the oviparous quadrupeds. And the explanation is that some of them in their breeding periods, and some all their life, live in holes.

  17 · Now the rest have bandy legs because they are soft-skinned, but the crayfish is hard-skinned and its limbs are for swimming and not for walking. Crabs, too, have their limbs bent obliquely, but not bandy like oviparous quadrupeds and [25] non-sanguineous polypods, because their limbs have a hard and shell-like skin, although they do not swim but live in holes; they live in fact on the ground. Moreover, their shape is round, and they have no
t a tail like the crayfish; a tail is useful to the crayfish for swimming, but the crab is not a swimming creature. [30] Further, it alone has its side equivalent to a hinder part, because it has many leading feet. The explanation of this is that its flexions are not forward nor its legs bandy. [714a1] We have given above the reason why its legs are not bandy, that is the hardness and shell-like character of its integument.

  For these reasons then it must lead off with all its legs and move obliquely; obliquely, because the flexion is oblique; and with all its legs, because otherwise the [5] limbs that were still would have got in the way of those that were moving.

  Fishes of the flat kind swim as one-eyed men walk; they have their natural shape distorted. Web-footed birds swim with their feet; because they take in air and breathe they are bipeds, but because they have their home in the water they are [10] webbed; by this arrangement their feet serve them instead of fins. They have their legs too, not like the rest of birds in the centre of their body, but rather set back. Their legs are short, and being set back are serviceable for swimming. The reason for their having short legs is that nature has added to their feet by subtracting from [15] the length of their limbs and instead of length has given stoutness to the legs and breadth to the feet. Broad feet are more useful than long for pushing away the water when they are swimming.

  18 · There is reason, too, for winged creatures having feet, but fish none. [20] The former have their home in the dry medium, and cannot remain always in mid air; they must therefore have feet. Fish on the contrary live in the wet medium, and take in water, not air. Fins are useful for swimming, but feet not. And if they had [714b1] both they would be non-sanguineous. There is a broad similarity between birds and fishes: birds have their wings on the superior part, similarly fish have two pectoral fins; again, birds have legs on their under parts and most fish have fins on the under [5] parts and near the pectorals. Birds, too, have a tail and fish a tail-fin.