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3
Of the psychic powers above enumerated some kinds of living things； as we have said； possess all； some less than all； others one only。 Those we have mentioned are the nutritive； the appetitive； the sensory； the locomotive； and the power of thinking。 Plants have none but the first； the nutritive； while another order of living things has this plus the sensory。 If any order of living things has the sensory； it must also have the appetitive； for appetite is the genus of which desire； passion； and wish are the species； now all animals have one sense at least； viz。 touch； and whatever has a sense has the capacity for pleasure and pain and therefore has pleasant and painful objects present to it； and wherever these are present； there is desire； for desire is just appetition of what is pleasant。 Further； all animals have the sense for food （for touch is the sense for food）； the food of all living things consists of what is dry； moist； hot； cold； and these are the qualities apprehended by touch； all other sensible qualities are apprehended by touch only indirectly。 Sounds； colours； and odours contribute nothing to nutriment； flavours fall within the field of tangible qualities。 Hunger and thirst are forms of desire； hunger a desire for what is dry and hot； thirst a desire for what is cold and moist； flavour is a sort of seasoning added to both。 We must later clear up these points； but at present it may be enough to say that all animals that possess the sense of touch have also appetition。 The case of imagination is obscure； we must examine it later。 Certain kinds of animals possess in addition the power of locomotion； and still another order of animate beings； i。e。 man and possibly another order like man or superior to him； the power of thinking； i。e。 mind。 It is now evident that a single definition can be given of soul only in the same sense as one can be given of figure。 For； as in that case there is no figure distinguishable and apart from triangle； &c。； so here there is no soul apart from the forms of soul just enumerated。 It is true that a highly general definition can be given for figure which will fit all figures without expressing the peculiar nature of any figure。 So here in the case of soul and its specific forms。 Hence it is absurd in this and similar cases to demand an absolutely general definition which will fail to express the peculiar nature of anything that is； or again； omitting this； to look for separate definitions corresponding to each infima species。 The cases of figure and soul are exactly parallel； for the particulars subsumed under the common name in both cases…figures and living beings…constitute a series； each successive term of which potentially contains its predecessor； e。g。 the square the triangle； the sensory power the self…nutritive。 Hence we must ask in the case of each order of living things； What is its soul； i。e。 What is the soul of plant； animal； man？ Why the terms are related in this serial way must form the subject of later examination。 But the facts are that the power of perception is never found apart from the power of self…nutrition； while…in plants…the latter is found isolated from the former。 Again； no sense is found apart from that of touch； while touch is found by itself； many animals have neither sight； hearing； nor smell。 Again； among living things that possess sense some have the power of locomotion； some not。 Lastly； certain living beings…a small minority…possess calculation and thought； for （among mortal beings） those which possess calculation have all the other powers above mentioned； while the converse does not hold…indeed some live by imagination alone； while others have not even imagination。 The mind that knows with immediate intuition presents a different problem。 It is evident that the way to give the most adequate definition of soul is to seek in the case of each of its forms for the most appropriate definition。
4
It is necessary for the student of these forms of soul first to find a definition of each； expressive of what it is； and then to investigate its derivative properties； &c。 But if we are to express what each is； viz。 what the thinking power is； or the perceptive； or the nutritive； we must go farther back and first give an account of thinking or perceiving； for in the order of investigation the question of what an agent does precedes the question； what enables it to do what it does。 If this is correct； we must on the same ground go yet another step farther back and have some clear view of the objects of each； thus we must start with these objects； e。g。 with food； with what is perceptible； or with what is intelligible。 It follows that first of all we must treat of nutrition and reproduction； for the nutritive soul is found along with all the others and is the most primitive and widely distributed power of soul； being indeed that one in virtue of which all are said to have life。 The acts in which it manifests itself are reproduction and the use of food…reproduction； I say； because for any living thing that has reached its normal development and which is unmutilated； and whose mode of generation is not spontaneous； the most natural act is the production of another like itself； an animal producing an animal； a plant a plant； in order that； as far as its nature allows； it may partake in the eternal and divine。 That is the goal towards which all things strive； that for the sake of which they do whatsoever their nature renders possible。 The phrase 'for the sake of which' is ambiguous； it may mean either （a） the end to achieve which； or （b） the being in whose interest； the act is done。 Since then no living thing is able to partake in what is eternal and divine by uninterrupted continuance （for nothing perishable can for ever remain one and the same）； it tries to achieve that end in the only way possible to it； and success is possible in varying degrees； so it remains not indeed as the self…same individual but continues its existence in something like itself…not numerically but specifically one。 The soul is the cause or source of the living body。 The terms cause and source have many senses。 But the soul is the cause of its body alike in all three senses which we explicitly recognize。 It is （a） the source or origin of movement； it is （b） the end； it is （c） the essence of the whole living body。 That it is the last； is clear； for in everything the essence is identical with the ground of its being； and here； in the case of living things； their being is to live； and of their being and their living the soul in them is the cause or source。 Further； the actuality of whatever is potential is identical with its formulable essence。 It is manifest that the soul is also the final cause of its body。 For Nature； like mind； always does whatever it does for the sake of something； which something is its end。 To that something corresponds in the case of animals the soul and in this it follows the order of nature； all natural bodies are organs of the soul。 This is true of those that enter into the constitution of plants as well as of those which enter into that of animals。 This shows that that the sake of which they are is soul。 We must here recall the two senses of 'that for the sake of which'； viz。 （a） the end to achieve which； and （b） the being in whose interest； anything is or is done。 We must maintain； further； that the soul is also the cause of the living body as the original source of local movement。 The power of locomotion is not found； however； in all living things。 But change of quality and change of quantity are also due to the soul。 Sensation is held to be a qualitative alteration； and nothing except what has soul in it is capable of sensation。 The same holds of the quantitative changes which constitute growth and decay； nothing grows or decays naturally except what feeds itself； and nothing feeds itself except what has a share of soul in it。 Empedocles is wrong in adding that growth in plants is to be explained； the downward rooting by the natural tendency of earth to travel downwards； and the upward branching by the similar natural tendency of fire to travel upwards。 For he misinterprets up and down； up and down are not for all things what they are for the whole Cosmos： if we are to distinguish and identify organs according to their functions； the roots of plants are analogous to the head in animals。 Further； we must ask what is the force that holds together the earth and the fire which tend to travel in contrary directions； if there is no counteracting force； they will be torn asunder； if there is； this must be the soul and the cause of nutrition and growth。 By some the element of fire is held to be the cause of nutrition and growth； for it alone of the primary bodies or elements is observed to feed and increase itself。 Hence the suggestion that in both plants and animals it is it which is the operative force。 A concurrent cause in a sense it certainly is； but not the principal cause； that is rather the soul； for while the growth of fire goes on without limit so long as there is a supply of fuel； in the case of all complex wholes formed in the course of nature there is a limit or ratio which determines