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have imagination and desire； but indefinitely？ Sensitive imagination； as we have said； is found in all animals； deliberative imagination only in those that are calculative： for whether this or that shall be enacted is already a task requiring calculation； and there must be a single standard to measure by； for that is pursued which is greater。 It follows that what acts in this way must be able to make a unity out of several images。 This is the reason why imagination is held not to involve opinion； in that it does not involve opinion based on inference； though opinion involves imagination。 Hence appetite contains no deliberative element。 Sometimes it overpowers wish and sets it in movement： at times wish acts thus upon appetite； like one sphere imparting its movement to another； or appetite acts thus upon appetite； i。e。 in the condition of moral weakness （though by nature the higher faculty is always more authoritative and gives rise to movement）。 Thus three modes of movement are possible。 The faculty of knowing is never moved but remains at rest。 Since the one premiss or judgement is universal and the other deals with the particular （for the first tells us that such and such a kind of man should do such and such a kind of act； and the second that this is an act of the kind meant； and I a person of the type intended）； it is the latter opinion that really originates movement； not the universal； or rather it is both； but the one does so while it remains in a state more like rest； while the other partakes in movement。
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The nutritive soul then must be possessed by everything that is alive； and every such thing is endowed with soul from its birth to its death。 For what has been born must grow； reach maturity； and decay…all of which are impossible without nutrition。 Therefore the nutritive faculty must be found in everything that grows and decays。 But sensation need not be found in all things that live。 For it is impossible for touch to belong either （1） to those whose body is uncompounded or （2） to those which are incapable of taking in the forms without their matter。 But animals must be endowed with sensation； since Nature does nothing in vain。 For all things that exist by Nature are means to an end； or will be concomitants of means to an end。 Every body capable of forward movement would； if unendowed with sensation； perish and fail to reach its end； which is the aim of Nature； for how could it obtain nutriment？ Stationary living things； it is true； have as their nutriment that from which they have arisen； but it is not possible that a body which is not stationary but produced by generation should have a soul and a discerning mind without also having sensation。 （Nor yet even if it were not produced by generation。 Why should it not have sensation？ Because it were better so either for the body or for the soul？ But clearly it would not be better for either： the absence of sensation will not enable the one to think better or the other to exist better。） Therefore no body which is not stationary has soul without sensation。 But if a body has sensation； it must be either simple or compound。 And simple it cannot be； for then it could not have touch； which is indispensable。 This is clear from what follows。 An animal is a body with soul in it： every body is tangible； i。e。 perceptible by touch； hence necessarily； if an animal is to survive； its body must have tactual sensation。 All the other senses； e。g。 smell； sight； hearing； apprehend through media； but where there is immediate contact the animal； if it has no sensation； will be unable to avoid some things and take others； and so will find it impossible to survive。 That is why taste also is a sort of touch； it is relative to nutriment； which is just tangible body； whereas sound； colour； and odour are innutritious； and further neither grow nor decay。 Hence it is that taste also must be a sort of touch； because it is the sense for what is tangible and nutritious。 Both these senses； then； are indispensable to the animal； and it is clear that without touch it is impossible for an animal to be。 All the other senses subserve well…being and for that very reason belong not to any and every kind of animal； but only to some； e。g。 those capable of forward movement must have them； for； if they are to survive； they must perceive not only by immediate contact but also at a distance from the object。 This will be possible if they can perceive through a medium； the medium being affected and moved by the perceptible object； and the animal by the medium。 just as that which produces local movement causes a change extending to a certain point； and that which gave an impulse causes another to produce a new impulse so that the movement traverses a medium the first mover impelling without being impelled； the last moved being impelled without impelling； while the medium （or media； for there are many） is both…so is it also in the case of alteration； except that the agent produces produces it without the patient's changing its place。 Thus if an object is dipped into wax； the movement goes on until submersion has taken place； and in stone it goes no distance at all； while in water the disturbance goes far beyond the object dipped： in air the disturbance is propagated farthest of all； the air acting and being acted upon； so long as it maintains an unbroken unity。 That is why in the case of reflection it is better； instead of saying that the sight issues from the eye and is reflected； to say that the air； so long as it remains one； is affected by the shape and colour。 On a smooth surface the air possesses unity； hence it is that it in turn sets the sight in motion； just as if the impression on the wax were transmitted as far as the wax extends。
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It is clear that the body of an animal cannot be simple； i。e。 consist of one element such as fire or air。 For without touch it is impossible to have any other sense； for every body that has soul in it must； as we have said； be capable of touch。 All the other elements with the exception of earth can constitute organs of sense； but all of them bring about perception only through something else； viz。 through the media。 Touch takes place by direct contact with its objects； whence also its name。 All the other organs of sense； no doubt； perceive by contact； only the contact is mediate： touch alone perceives by immediate contact。 Consequently no animal body can consist of these other elements。 Nor can it consist solely of earth。 For touch is as it were a mean between all tangible qualities； and its organ is capable of receiving not only all the specific qualities which characterize earth； but also the hot and the cold and all other tangible qualities whatsoever。 That is why we have no sensation by means of bones； hair； &c。； because they consist of earth。 So too plants； because they consist of earth； have no sensation。 Without touch there can be no other sense； and the organ of touch cannot consist of earth or of any other single element。 It is evident； therefore； that the loss of this one sense alone must bring about the death of an animal。 For as on the one hand nothing which is not an animal can have this sense； so on the other it is the only one which is indispensably necessary to what is an animal。 This explains； further； the following difference between the other senses and touch。 In the case of all the others excess of intensity in the qualities which they apprehend； i。e。 excess of intensity in colour； sound； and smell； destroys not the but only the organs of the sense （except incidentally； as when the sound is accompanied by an impact or shock； or where through the objects of sight or of smell certain other things are set in motion； which destroy by contact）； flavour also destroys only in so far as it is at the same time tangible。 But excess of intensity in tangible qualities； e。g。 heat； cold； or hardness； destroys the animal itself。 As in the case of every sensible quality excess destroys the organ； so here what is tangible destroys touch； which is the essential mark of life； for it has been shown that without touch it is impossible for an animal to be。 That is why excess in intensity o