on the soul-第21章
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ginates local movement of the animal。 The movement of growth and decay； being found in all living things； must be attributed to the faculty of reproduction and nutrition； which is common to all： inspiration and expiration； sleep and waking； we must consider later： these too present much difficulty： at present we must consider local movement； asking what it is that originates forward movement in the animal。 That it is not the nutritive faculty is obvious； for this kind of movement is always for an end and is accompanied either by imagination or by appetite； for no animal moves except by compulsion unless it has an impulse towards or away from an object。 Further； if it were the nutritive faculty； even plants would have been capable of originating such movement and would have possessed the organs necessary to carry it out。 Similarly it cannot be the sensitive faculty either； for there are many animals which have sensibility but remain fast and immovable throughout their lives。 If then Nature never makes anything without a purpose and never leaves out what is necessary （except in the case of mutilated or imperfect growths； and that here we have neither mutilation nor imperfection may be argued from the facts that such animals （a） can reproduce their species and （b） rise to completeness of nature and decay to an end）； it follows that； had they been capable of originating forward movement； they would have possessed the organs necessary for that purpose。 Further； neither can the calculative faculty or what is called 'mind' be the cause of such movement； for mind as speculative never thinks what is practicable； it never says anything about an object to be avoided or pursued； while this movement is always in something which is avoiding or pursuing an object。 No； not even when it is aware of such an object does it at once enjoin pursuit or avoidance of it； e。g。 the mind often thinks of something terrifying or pleasant without enjoining the emotion of fear。 It is the heart that is moved （or in the case of a pleasant object some other part）。 Further； even when the mind does command and thought bids us pursue or avoid something； sometimes no movement is produced； we act in accordance with desire； as in the case of moral weakness。 And； generally； we observe that the possessor of medical knowledge is not necessarily healing； which shows that something else is required to produce action in accordance with knowledge； the knowledge alone is not the cause。 Lastly； appetite too is incompetent to account fully for movement； for those who successfully resist temptation have appetite and desire and yet follow mind and refuse to enact that for which they have appetite。
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These two at all events appear to be sources of movement： appetite and mind （if one may venture to regard imagination as a kind of thinking； for many men follow their imaginations contrary to knowledge； and in all animals other than man there is no thinking or calculation but only imagination）。 Both of these then are capable of originating local movement； mind and appetite： （1） mind； that is； which calculates means to an end； i。e。 mind practical （it differs from mind speculative in the character of its end）； while （2） appetite is in every form of it relative to an end： for that which is the object of appetite is the stimulant of mind practical； and that which is last in the process of thinking is the beginning of the action。 It follows that there is a justification for regarding these two as the sources of movement； i。e。 appetite and practical thought； for the object of appetite starts a movement and as a result of that thought gives rise to movement； the object of appetite being it a source of stimulation。 So too when imagination originates movement； it necessarily involves appetite。 That which moves therefore is a single faculty and the faculty of appetite； for if there had been two sources of movement…mind and appetite…they would have produced movement in virtue of some common character。 As it is； mind is never found producing movement without appetite （for wish is a form of appetite； and when movement is produced according to calculation it is also according to wish）； but appetite can originate movement contrary to calculation； for desire is a form of appetite。 Now mind is always right； but appetite and imagination may be either right or wrong。 That is why； though in any case it is the object of appetite which originates movement； this object may be either the real or the apparent good。 To produce movement the object must be more than this： it must be good that can be brought into being by action； and only what can be otherwise than as it is can thus be brought into being。 That then such a power in the soul as has been described； i。e。 that called appetite； originates movement is clear。 Those who distinguish parts in the soul； if they distinguish and divide in accordance with differences of power； find themselves with a very large number of parts； a nutritive； a sensitive； an intellective； a deliberative； and now an appetitive part； for these are more different from one another than the faculties of desire and passion。 Since appetites run counter to one another； which happens when a principle of reason and a desire are contrary and is possible only in beings with a sense of time （for while mind bids us hold back because of what is future； desire is influenced by what is just at hand： a pleasant object which is just at hand presents itself as both pleasant and good； without condition in either case； because of want of foresight into what is farther away in time）； it follows that while that which originates movement must be specifically one； viz。 the faculty of appetite as such （or rather farthest back of all the object of that faculty； for it is it that itself remaining unmoved originates the movement by being apprehended in thought or imagination）； the things that originate movement are numerically many。 All movement involves three factors； （1） that which originates the movement； （2） that by means of which it originates it； and （3） that which is moved。 The expression 'that which originates the movement' is ambiguous： it may mean either （a） something which itself is unmoved or （b） that which at once moves and is moved。 Here that which moves without itself being moved is the realizable good； that which at once moves and is moved is the faculty of appetite （for that which is influenced by appetite so far as it is actually so influenced is set in movement； and appetite in the sense of actual appetite is a kind of movement）； while that which is in motion is the animal。 The instrument which appetite employs to produce movement is no longer psychical but bodily： hence the examination of it falls within the province of the functions common to body and soul。 To state the matter summarily at present； that which is the instrument in the production of movement is to be found where a beginning and an end coincide as e。g。 in a ball and socket joint； for there the convex and the concave sides are respectively an end and a beginning （that is why while the one remains at rest； the other is moved）： they are separate in definition but not separable spatially。 For everything is moved by pushing and pulling。 Hence just as in the case of a wheel； so here there must be a point which remains at rest； and from that point the movement must originate。 To sum up； then； and repeat what I have said； inasmuch as an animal is capable of appetite it is capable of self…movement； it is not capable of appetite without possessing imagination； and all imagination is either （1） calculative or （2） sensitive。 In the latter an animals； and not only man； partake。
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We must consider also in the case of imperfect animals； sc。 those which have no sense but touch； what it is that in them originates movement。 Can they have imagination or not？ or desire？ Clearly they have feelings of pleasure and pain； and if they have these they must have desire。 But how can they have imagination？ Must not we say that； as their movements are indefinite； they have imagination and desire； but indefinitely？ Sensitive imagination； as we have said； is found i
