Since plants nourish themselves they have the faculty of nutrition. And because it is of the nature of plants to grow, it follows that they have the faculty of growth. Again, since it is the nature of certain plants to reproduce their like and to be reproduced by their like, they have a reproductive faculty. The reproductive faculty is different from the faculty of nutrition, for unripe fruits possess the nutritive but not the reproductive faculty; just as they possess the faculty of growth, but not that of reproduction. Similarly, the faculty of nutrition differs from that of growth. Do you not see that decrepit animals have the nutritive faculty but lack that of growth?
The nutritive faculty transmits food and replaces what has been dissolved with it; the faculty of growth increases the substance of the main structural organs in length, breadth, and depth, not haphazard but in such a way that they can reach the utmost perfection of growth. The reproductive faculty gives the matter the form of the thing; it separates from the parent body a part in which a faculty derived from its origin inheres and which, when the matter and the place which are prepared to receive its activity are present, performs its functions.
It will be evident from the foregoing that all vegetable, animal, and human functions are due to faculties over and above bodily functions, and even over and above the nature of the mixture itself.
After the plant comes the animal, which emerges from a compound of elements whose organic nature is much nearer to the mean than the previous two and is therefore prepared to receive the animal soul, having passed through the stage of the vegetable soul. And so the nearer it approaches the mean the greater is its capacity for receiving yet another psychical faculty more refined than the previous one.
The soul is like a single genus divisible in some way into three parts. The first is the vegetable soul, which is the first entelechy of a natural body possessing organs in so far as it is reproduced, grows, and assimilates nourishment. Food is a body whose function it is to become similar to the nature of the body whose food it is said to be, and adds to that body either in exact proportion or more or less what is dissolved.
The second is the animal soul, which is the first entelechy of a natural body possessing organs in so far as it perceives individuals and moves by volition.
The third is the human soul, which is the first entelechy of a natural body possessing organs in so far as it acts by rational choice and rational deduction, and in so far as it perceives universals.
The vegetable soul has three faculties. First, the nutritive faculty which transforms another body into a body similar to that in which it is itself present, and replaces what has been dissolved. Secondly, the faculty of growth which increases every aspect of the body in which it resides, by length, breadth, and depth in proportion to the quantity necessary to make it attain its perfection in growth. Thirdly, the reproductive faculty which takes from the body in which it resides a part which is potentially similar to it and acts upon it with the help of other similar bodies, generating and mixing them so as to render that part actually similar to the body (to which it had been only potentially similar).
The perceptive faculty can be divided into two parts, the external sense and the internal sense. The external senses are the five or eight senses. One of them is sight, which is a faculty located in the concave nerve; it perceives the image of the forms of coloured bodies imprinted on the vitreous humour. These forms are transmitted through actually transparent media to polished surfaces. The second is the sense of hearing, which is a faculty located in the nerves distributed over the surface of the ear-hole; it perceives the form of what is transmitted to it by the vibration of the air which is compressed between two objects, one striking and the other being struck, the latter offering it resistance so as to set up vibrations in the air which produce the sound. This vibration of the air outside reaches the air which lies motionless and compressed in the cavity of the ear, moving it in a way similar to that in which it is itself moved. Its waves touch that nerve, and so it is heard.
The third sense is that of smell, a faculty located in the two protuberances of the front part of the brain which resemble the two nipples of the breasts. It perceives the odour conveyed to it by inhaled air, which is either mixed with the vapour in the air or is imprinted on it through qualitative change in the air produced by an odorous body.
The fourth sense is that of taste, a faculty located in the nerves distributed over the tongue, which perceives the taste dissolved from bodies touching it and mingling with the saliva it contains, thus producing a qualitative change in the tongue itself.
The fifth sense is that of touch, which is a faculty distributed over the entire skin and flesh of the body. The nerves perceive what touches them and are affected when it is opposed to them in quality, and changes are then wrought in their constitution or structure.
Probably this faculty is not one species but a genus including four faculties which are all distributed throughout the skin. The first of them judges the opposition between hot and cold; the second that between dry and moist; the third that between hard and soft; and the fourth that between rough and smooth. But their coexistence in the same organ gives the false impression that they are essentially one.
The forms of all the sensibles reach the organs of sense and are imprinted on them, and then the faculty of sensation perceives them. This is almost evident in touch, taste, smell, and hearing. But concerning sight, a different view has been maintained, for some people have thought that something issues from the eye, meets the object of sight, takes its form from without and that this constitutes the act of seeing. They often call the thing which according to them issues from the eye, light.
But true philosophers hold the view that when an actually transparent body, i.e. a body which has no colour, intervenes between the eye and the object of sight, the exterior form of the coloured body on which light is falling is transmitted to the pupil of the eye and so the eye perceives it.
This transmission is similar to the transmission of colours by means of light being refracted from a coloured thing and giving its colour to another body. The resemblance is not complete, however, for the former is more like an image in a mirror.
The absurdity of the view that light issues from the eye is shown by the following consideration. What emanates is either a body or a non-body. If it is not a body it is absurd to attribute motion and change of place to it, except figuratively in that there may be a power in the eye which transforms the air and other things it encounters into some sort of quality, so that it may be said that this quality "came out of the eye." Likewise, it is absurd to hold the view that it is a body, because if so then either
(1) it will remain intact, issuing from the eye and reaching to the sphere of the fixed stars. In this case there will have emerged from the eye, despite its smallness, a conical body of immense size, which will have compressed the air and repulsed all the heavenly bodies, or it will have traversed an empty space. Both these views are manifestly absurd. OrAgain, if the sensed object is seen through the base of the conical emanating body which touches it, and not through the angle, it will necessarily follow that the shape and magnitude of the object perceived at a distance will also be perceptible as well as its colour. This is because the percipient subject comes in contact with it and encompasses it. But if it is perceived through the angle, I mean the section between the vitrium and the hypothetical cone, then the remoter the object the smaller will be the angle and also the common section, and consequently the form imprinted on it will also be smaller and will be so perceived. Sometimes the angle will be so small that the object will fail to be perceived and so the form will not be seen at all.
(2) it will be dispersed, diffused and split up. In that case the percipient animal will of necessity feel something being detached from him and then dispersed and diffused; also, he will perceive the spots where that ray falls to the exclusion of the spots where it does not fall, so that he will only partially perceive the body, sensing some points here and there but missing the major part. Or
(3) this emanating body is united with the air and the heavens and becomes one with them, so that the uniform whole is like one organ of the animal. In this case the uniform whole in its entirety will possess sensation. This is a most peculiar change indeed! It follows necessarily that if many eyes co-operate, it will be more powerful. Thus a man when in the company of others would have keener sight than when alone, for many people can effect a more powerful change than a single person. Again, this emanating body will necessarily be either simple or composite, and its composite nature will also be of a particular kind. Its motion then must be either voluntary or natural. But we know that this movement is not voluntary and by choice, although the opening and closing of the eyelids are voluntary. The only remaining alternative is that the movement is natural. But the simple natural movement will be only in one direction, not in many; and so the composite movement will also be, according to the dominant element, only in one direction, not in many. But it is not so with this movement according to those who support the theory of the "issuing body."
As for the second part, namely that the emanating something is not a body but an accident or a quality, this "changing" or "being changed" will inevitably be more powerful with the increase of the percipient subjects. In that case the same absurdity which we mentioned before will arise. Again, the air will either be merely a medium of transmission or percipient in itself. If it is only a medium of transmission and not percipient, then, as we maintain, perception takes place in the pupil of the eye and not outside it. But if the percipient is the air, then the same absurdity which we have already mentioned will be repeated; and it will necessarily follow that whenever there is commotion or disturbance in the air, sight will be distorted with the renewal of "change" and the renewed action of the percipient in perceiving one thing after another, just as when a man runs in calm air his perception of minute things is confused. All this shows that sight is not due to something issuing from us towards the sensed object. It must therefore be due to something coming towards us from the sensed object; since this is not the body of the object, it must be its form. If this view were not correct, the creation of the eye with all its strata and humours and their respective shape and structure would be useless.
It is also possible to attribute morals to the bodily faculties. But if the latter predominate they are in an active state, while the practical intelligence is in a passive one. Thus the same thing produces morals in both. But if the practical intelligence predominates, it is in an active state while the bodily faculties are in a passive one, and this is morals in the strict sense (even so there would be two dispositions or moral characters); or character is only one with two different relationships. If we examine them more closely the reason why morals are attributed to this faculty is that the human soul, as will be shown later, is a single substance which is related to two planes the one higher and the other lower than itself. It has special faculties which establish the relationship between itself and each plane: the practical faculty which the human soul possesses in relation to the lower plane, which is the body, and its control and management; and the theoretical faculty in relation to the higher plane, from which it passively receives and acquires intelligibles. It is as if our soul has two faces: one turned towards the body and it must not be influenced by any requirements of the bodily nature; and the other turned towards the higher principles, and it must always be ready to receive from what is There in the Higher Plane and to be influenced by it. So much for the practical faculty.
What proves this is the evident fact that the intelligible truths are acquired only when the middle term of a syllogism is obtained. This may be done in two ways: sometimes through intuition, which is an act of mind by which the mind itself immediately perceives the middle term. This power of intuition is quickness of apprehension. But sometimes the middle term is acquired through instruction, although even the first principles of instruction are obtained through intuition, since all knowledge can be reduced ultimately to certain intuitive principles handed down by those who first accepted them to their students.
It is possible that a man may find the truth within himself, and that the syllogism may be effected in his mind without any teacher. This varies both quantitatively and qualitatively; quantitatively, because some people possess a greater number of middle terms which they have discovered themselves; and qualitatively, because some people find the term more quickly than others. Now since these differences are unlimited and always vary in degrees of intensity, and since their lowest point is reached in men who are wholly without intuition, so their highest point must be reached in people who possess intuition regarding all or most problems, or in people who have intuition in the shortest possible time. Thus there might be a man whose soul has such an intense purity and is so firmly linked to the rational principles that he blazes with intuition, i.e. with the receptivity of inspiration coming from the active intelligence concerning everything. So the forms of all things contained in the active intelligence are imprinted on his soul either all at once or nearly so, not that he accepts them merely on authority but on account of their logical order which encompasses all the middle terms. For beliefs accepted on authority concerning those things which are known only through their causes possess no rational certainty. This is a kind of prophetic inspiration, indeed its highest form and the one most fitted to be called Divine Power; and it is the highest human faculty.
The animal faculties in their entirety are served by the vegetable faculties, of which the reproductive is the first in rank and the highest one. The faculty of growth serves the reproductive, and the nutritive faculty serves them both. The four "natural" faculties of digestion, retention, assimilation, and excretion are subservient to all these. The digestive faculty is served on the one hand by the retentive and the assimilative, and on the other by the excretive. The four physical qualities serve these, with cold subservient to heat, while dryness and moisture serve them both. This is the last degree of the faculties.
I say that it is also impossible for souls to have numerically one essence, for when two bodies come into existence two souls also come into existence in them. Then either
these two souls are two parts of the same single soul, in which case one single thing which does not possess any magnitude and bulk would be potentially divisible. This is manifestly absurd according to the principles established in physics. OrIt is thus proved that the soul comes into existence whenever a body does so fit to be used by it. The body which thus comes into being is the kingdom and instrument of the soul. In the very disposition of the substance of the soul which comes into existence together with a certain body a body, that is to say, with the appropriate qualities to make it suitable to receive the soul which takes its origin from the first principles there is a natural yearning to occupy itself with that body, to use it, control it, and be attracted by it. This yearning binds the soul specially to this body, and turns it away from other bodies different from it in nature so that the soul does not contact them except through it. Thus when the principle of its individualization, namely, its peculiar dispositions, occurs to it, it becomes an individual. These dispositions determine its attachment to that particular body and form the relationship of their mutual suitability, although this relationship and its condition may be obscure to us. The soul achieves its first entelechy through the body; its subsequent development, however, does not depend on the body but on its own nature.
a soul which is numerically one would be in two bodies. This also does not require much effort to refute.
But after their separation from their bodies the souls remain individual owing to the different matters in which they had been, and owing to the times of their birth and their different dispositions due to their bodies which necessarily differ because of their peculiar conditions.
Thus the attachment of the soul to the body is not the attachment of an effect to a necessary cause. The truth is that the body and the temperament are an accidental cause of the soul, for when the matter of a body suitable to become the instrument of the soul and its proper subject comes into existence, the separate causes bring into being the individual soul, and that is how the soul originates from them. This is because it is impossible to bring arbitrarily into being different souls without any specific cause. Besides, the soul does not admit of numerical multiplicity, as we have shown. Again, whenever a new thing comes into being, it must be preceded by a matter which is prepared to receive it or to have a relationship with it, as has been shown in the other sciences. Again, if an individual soul were to come into being without an instrument through which it acts and attains perfection, its being would be purposeless; but there is nothing purposeless in nature. In truth, when the suitability and preparation for such a relationship exist in the instrument, it becomes necessary that such a thing as a soul should originate from the separate causes.
But if the existence of one thing necessitates the existence of another, the corruption of the former does not necessarily entail that of the latter. This happens only where its very being subsists through or in that thing. Many things originating from other things survive the latter's corruption; when their being does not subsist in them, and especially when they owe their existence to something other than what was merely preparatory for the emanation of their being. And the being of the soul does in fact emanate from something different from the body and bodily functions, as we have shown; its source of emanation must be something different from the body. Thus when the soul owes its being to that other thing and only the time of its realization to the body, its being would be independent of the body which is only its accidental cause; it cannot then be said that they have a mutual relationship which would necessitate the body preceding the soul as its necessary cause.
Let us turn to the third division which we mentioned in the beginning, namely, that the attachment of the soul to the body might be in the sense that the soul is prior to the body in existence. Now in that case the priority will be either temporal as well as essential, and so the soul's being could not possibly be attached to the body since it precedes the body in time, or the priority will be only essential and not temporal, for in time the soul will not be separate from the body. This sort of priority means that when the prior entity comes into existence, the being of the posterior entity must follow from it. Then the prior entity cannot exist, if the posterior is supposed to be non-existent. I do not say that the supposition of the non-existence of the posterior necessitates the nonexistence of the prior, but that the posterior cannot be non-existent except when first something has naturally happened to the prior which has made it nonexistent, too. Thus it is not the supposition of the non-existence of the posterior entity which necessitates the nonexistence of the prior, but the supposition of the non-existence of the prior itself, for the posterior can be supposed to be non-existent only after the prior itself has ceased to exist. This being so, it follows that the cause of non-existence must occur in the substance of the soul necessitating the body's corruption along with it, and that the body cannot be corrupted through a cause special to itself. But in fact the corruption of the body does take place through a cause special to itself, namely, through changes in its composition and its temperament. Thus it is false to hold that the soul is attached to the body as essentially prior to it, and that at the same time the body is indeed corrupted through a cause in itself; so no such relationship subsists between the two.
This being so, all the forms of attachment between the body and the soul have proved to be false and it only remains that the soul, in its being, has no relationship with the body but is related with other principles which are not subject to change or corruption.
As for the proposition that the soul does not admit of corruption at all, I say that there is another conclusive reason for the immortality of the soul. Everything which might be corrupted through some cause has in itself the potentiality of corruption and, before corruption, has the actuality of persistence. But it is absurd that a single thing in the same sense should possess both, the potentiality of corruption and the actuality of persistence; its potentiality of corruption cannot be due to its actual persistence, for the concept of potentiality is contrary to that of actuality. Also, the relation of this potentiality is opposed to the relation of this actuality, for the one is related with corruption, the other with persistence. These two concepts, then, are attributable to two different factors in the concrete thing. Hence we say that the actuality of persistence and the potentiality of corruption may be combined in composite things and in such simple things as subsist in composite ones. But these two concepts cannot come together in simple things whose essence is separate. I say in another absolute sense that these two concepts cannot exist together in a simple thing whose essence is unitary. This is because everything which persists and has the potentiality of corruption also has the potentiality of persistence, since its persistence is not necessary. When it is not necessary, it is possible; and possibility is of the nature of potentiality. Thus the potentiality of persistence is in its very substance. But, of course, it is clear that the actuality of persistence of a thing is not the same as its potentiality of persistence. Thus its actuality of persistence is a fact which happens to the body which has the potentiality of persistence. Therefore that potentiality does not belong to something actual but to something of which actual existence is only an accident and does not constitute its real essence. From this it necessarily follows that its being is composed of a factor the possession of which gives actual existence to it (this factor is the form in every concrete existent), and another factor which attains this actual existence but which in itself has only the potentiality of existence (and this factor is the matter in the concrete existent).
So if the soul is absolutely simple and is not divisible
into matter and form, it will not admit of corruption. But if it is composite,
let us leave the composite and consider only the substance which is its
matter. We say: either that matter will continue to be divisible and so
the same analysis will go on being applied to it and we shall then have
a regress ad infinitum,
which is absurd; or this substance and base
will never cease to exist. But if so, then our present discourse is devoted
to this factor which is the base and origin (i.e. the substance) and not
to the composite thing which is composed of this factor and some other.
So it is clear that everything which is simple and not composite, or which
is the origin and base (i.e. the substance) of the composite thing, cannot
in itself possess both the actuality of persistence and the potentiality
of corruption. If it has the potentiality of corruption, it cannot possibly
have the actuality of persistence, and if it has the actuality of persistence
and existence, it cannot have the potentiality of corruption. Obviously,
then, the substance of the soul does not have the potentiality of corruption.
Of those things which come to be and are corrupted, the corruptible is
only the concrete composite. The potentiality of corruption and of persistence
at the same time does not belong to something which gives unity to the
composite, but to the matter which potentially admits of both contraries.
So the corruptible composite as such possesses neither the potentiality
of persistence nor that of corruption, let alone both. As to the matter
itself, it either has persistence not due to any potentiality, which gives
it the capacity for persistence as some people think or it has persistence
through a potentiality which gives it persistence, but does not have the
potentiality of corruption; this latter being something which it acquires.
The potentiality of corruption of simple entities which subsist in matter
is due to matter and is not in their own substance. The argument which
proves that everything which comes to exist passes away on account of the
finitude of the potentialities of persistence and corruption is relevant
only to those things whose being is composed of matter and form. Matter
has the potentiality that this form may persist in it, and at the same
time the potentiality that this form may cease to exist in it. It is then
obvious that the soul is absolutely incorruptible. This is the point which
we wanted to make, and this is what we wanted to prove.