Summa Th. I EN Qu.77 a.6

Article: 6 Whether the powers of the soul flow from its essence?

Objection: 1. It would seem that the powers of the soul do not flow from its essence. For different things do not proceed from one simple thing. But the essence of the soul is one and simple. Since, therefore, the powers of the soul are many and various, they cannot proceed from its essence.

2. Further, that from which a thing proceeds is its cause. But the essence of the soul cannot be said to be the cause of the powers; as is clear if one considers the different kinds of causes. Therefore the powers of the soul do not flow from its essence.

3. Further, emanation involves some sort of movement. But nothing is moved by itself, as the Philosopher proves (Phys. vii, 1,2); except, perhaps, by reason of a part of itself, as an animal is said to be moved by itself, because one part thereof moves and another is moved. Neither is the soul moved, as the Philosopher proves (De Anima i, 4). Therefore the soul does not produce its powers within itself.

On the contrary The powers of the soul are its natural properties. But the subject is the cause of its proper accidents; whence also it is included in the definition of accident, as is clear from Metaph. vii (Did. vi, 4). Therefore the powers of the soul proceed from its essence as their cause.

I answer that The substantial and the accidental form partly agree and partly differ. They agree in this, that each is an act; and that by each of them something is after a manner actual. They differ, however, in two respects. First, because the substantial form makes a thing to exist absolutely, and its subject is something purely potential. But the accidental form does not make a thing to exist absolutely but to be such, or so great, or in some particular condition; for its subject is an actual being. Hence it is clear that actuality is observed in the substantial form prior to its being observed in the subject: and since that which is first in a genus is the cause in that genus, the substantial form causes existence in its subject. On the other hand, actuality is observed in the subject of the accidental form prior to its being observed in the accidental form; wherefore the actuality of the accidental form is caused by the actuality of the subject. So the subject, forasmuch as it is in potentiality, is receptive of the accidental form: but forasmuch as it is in act, it produces it. This I say of the proper and "per se" accident; for with regard to the extraneous accident, the subject is receptive only, the accident being caused by an extrinsic agent. Secondly, substantial and accidental forms differ, because, since that which is the less principal exists for the sake of that which is the more principal, matter therefore exists on account of the substantial form; while on the contrary, the accidental form exists on account of the completeness of the subject.

Now it is clear, from what has been said (Article [5]), that either the subject of the soul's powers is the soul itself alone, which can be the subject of an accident, forasmuch as it has something of potentiality, as we have said above (Article [1], ad 6); or else this subject is the composite. Now the composite is actual by the soul. Whence it is clear that all the powers of the soul, whether their subject be the soul alone, or the composite, flow from the essence of the soul, as from their principle; because it has already been said that the accident is caused by the subject according as it is actual, and is received into it according as it is in potentiality.

Reply to Objection: 1. From one simple thing many things may proceed naturally, in a certain order; or again if there be diversity of recipients. Thus, from the one essence of the soul many and various powers proceed; both because order exists among these powers; and also by reason of the diversity of the corporeal organs.

2. The subject is both the final cause, and in a way the active cause, of its proper accident. It is also as it were the material cause, inasmuch as it is receptive of the accident. From this we may gather that the essence of the soul is the cause of all its powers, as their end, and as their active principle; and of some as receptive thereof.

3. The emanation of proper accidents from their subject is not by way of transmutation, but by a certain natural resultance; thus one thing results naturally from another, as color from light.

Article: 7 Whether one power of the soul arises from another?

Objection: 1. It would seem that one power of the soul does not arise from another. For if several things arise together, one of them does not arise from another. But all the powers of the soul are created at the same time with the soul. Therefore one of them does not arise from another.

2. Further, the power of the soul arises from the soul as an accident from the subject. But one power of the soul cannot be the subject of another; because nothing is the accident of an accident. Therefore one power does not arise from another.

3. Further, one opposite does not arise from the other opposite; but everything arises from that which is like it in species. Now the powers of the soul are oppositely divided, as various species. Therefore one of them does not proceed from another.

On the contrary Powers are known by their actions. But the action of one power is caused by the action of another power, as the action of the imagination by the action of the senses. Therefore one power of the soul is caused by another.

I answer that In those things which proceed from one according to a natural order, as the first is the cause of all, so that which is nearer to the first is, in a way, the cause of those which are more remote. Now it has been shown above (Article [4]) that among the powers of the soul there are several kinds of order. Therefore one power of the soul proceeds from the essence of the soul by the medium of another. But since the essence of the soul is compared to the powers both as a principle active and final, and as a receptive principle, either separately by itself, or together with the body; and since the agent and the end are more perfect, while the receptive principle, as such, is less perfect; it follows that those powers of the soul which precede the others, in the order of perfection and nature, are the principles of the others, after the manner of the end and active principle. For we see that the senses are for the sake of the intelligence, and not the other way about. The senses, moreover, are a certain imperfect participation of the intelligence; wherefore, according to their natural origin, they proceed from the intelligence as the imperfect from the perfect. But considered as receptive principles, the more perfect powers are principles with regard to the others; thus the soul, according as it has the sensitive power, is considered as the subject, and as something material with regard to the intelligence. On this account, the more imperfect powers precede the others in the order of generation, for the animal is generated before the man.

Reply to Objection: 1. As the power of the soul flows from the essence, not by a transmutation, but by a certain natural resultance, and is simultaneous with the soul, so is it the case with one power as regards another.

2. An accident cannot of itself be the subject of an accident; but one accident is received prior to another into substance, as quantity prior to quality. In this sense one accident is said to be the subject of another; as surface is of color, inasmuch as substance receives an accident through the means of another. The same thing may be said of the powers of the soul.

3. The powers of the soul are opposed to one another, as perfect and imperfect; as also are the species of numbers and figures. But this opposition does not prevent the origin of one from another, because imperfect things naturally proceed from perfect things.

Article: 8 Whether all the powers remain in the soul when separated from the body?

Objection: 1. It would seem that all the powers of the soul remain in the soul separated from the body. For we read in the book De Spiritu et Anima that "the soul withdraws from the body, taking with itself sense and imagination, reason and intelligence, concupiscibility and irascibility."

2. Further, the powers of the soul are its natural properties. But properties are always in that to which they belong; and are never separated from it. Therefore the powers of the soul are in it even after death.

3. Further, the powers even of the sensitive soul are not weakened when the body becomes weak; because, as the Philosopher says (De Anima i, 4), "If an old man were given the eye of a young man, he would see even as well as a young man." But weakness is the road to corruption. Therefore the powers of the soul are not corrupted when the body is corrupted, but remain in the separated soul.

4. Further, memory is a power of the sensitive soul, as the Philosopher proves (De Memor. et Remin. 1). But memory remains in the separated soul; for it was said to the rich glutton whose soul was in hell: "Remember that thou didst receive good things during thy lifetime" (Lc 16,25). Therefore memory remains in the separated soul; and consequently the other powers of the sensitive part.

5. Further, joy and sorrow are in the concupiscible part, which is a power of the sensitive soul. But it is clear that separate souls grieve or rejoice at the pains or rewards which they receive. Therefore the concupiscible power remains in the separate soul.

6. Further, Augustine says (Gn ad lit. xii, 32) that, as the soul, when the body lies senseless, yet not quite dead, sees some things by imaginary vision; so also when by death the soul is quite separate from the body. But the imagination is a power of the sensitive part. Therefore the power of the sensitive part remains in the separate soul; and consequently all the other powers.

On the contrary It is said (De Eccl. Dogm. xix) that "of two substances only does man consist; the soul with its reason, and the body with its senses." Therefore the body being dead, the sensitive powers do not remain.

I answer that As we have said already (Articles [5],6,7), all the powers of the soul belong to the soul alone as their principle. But some powers belong to the soul alone as their subject; as the intelligence and the will. These powers must remain in the soul, after the destruction of the body. But other powers are subjected in the composite; as all the powers of the sensitive and nutritive parts. Now accidents cannot remain after the destruction of the subject. Wherefore, the composite being destroyed, such powers do not remain actually; but they remain virtually in the soul, as in their principle or root.

So it is false that, as some say, these powers remain in the soul even after the corruption of the body. It is much more false that, as they say also, the acts of these powers remain in the separate soul; because these powers have no act apart from the corporeal organ.

Reply to Objection: 1. That book has no authority, and so what is there written can be despised with the same facility as it was said; although we may say that the soul takes with itself these powers, not actually but virtually.

2. These powers, which we say do not actually remain in the separate soul, are not the properties of the soul alone, but of the composite.

3. These powers are said not to be weakened when the body becomes weak, because the soul remains unchangeable, and is the virtual principle of these powers.

4. The recollection spoken of there is to be taken in the same way as Augustine (De Trin. x, 11; xiv, 7) places memory in the mind; not as a part of the sensitive soul.

5. In the separate soul, sorrow and joy are not in the sensitive, but in the intellectual appetite, as in the angels.

6. Augustine in that passage is speaking as inquiring, not as asserting. Wherefore he retracted some things which he had said there (Retrac. ii, 24).


We next treat of the powers of the soul specifically. The theologian, however, has only to inquire specifically concerning the intellectual and appetitive powers, in which the virtues reside. And since the knowledge of these powers depends to a certain extent on the other powers, our consideration of the powers of the soul taken specifically will be divided into three parts: first, we shall consider those powers which are a preamble to the intellect; secondly, the intellectual powers; thirdly, the appetitive powers.

Under the first head there are four points of inquiry:

(1) The powers of the soul considered generally;

(2) The various species of the vegetative part;

(3) The exterior senses;

(4) The interior senses.

Article: 1 Whether there are to be distinguished five genera of powers in the soul?

Objection: 1. It would seem that there are not to be distinguished five genera of powers in the soul---namely, vegetative, sensitive, appetitive, locomotive, and intellectual. For the powers of the soul are called its parts. But only three parts of the soul are commonly assigned---namely, the vegetative soul, the sensitive soul, and the rational soul. Therefore there are only three genera of powers in the soul, and not five.

2. Further, the powers of the soul are the principles of its vital operations. Now, in four ways is a thing said to live. For the Philosopher says (De Anima ii, 2): "In several ways a thing is said to live, and even if only one of these is present, the thing is said to live; as intellect and sense, local movement and rest, and lastly, movement of decrease and increase due to nourishment." Therefore there are only four genera of powers of the soul, as the appetitive is excluded.

3. Further, a special kind of soul ought not to be assigned as regards what is common to all the powers. Now desire is common to each power of the soul. For sight desires an appropriate visible object; whence we read (Si 40,22): "The eye desireth favor and beauty, but more than these green sown fields." In the same way every other power desires its appropriate object. Therefore the appetitive power should not be made a special genus of the powers of the soul.

4. Further, the moving principle in animals is sense, intellect or appetite, as the Philosopher says (De Anima iii, 10). Therefore the motive power should not be added to the above as a special genus of soul.

On the contrary The Philosopher says (De Anima ii, 3), "The powers are the vegetative, the sensitive, the appetitive, the locomotion, and the intellectual."

I answer that, There are five genera of powers of the soul, as above numbered. Of these, three are called souls, and four are called modes of living. The reason of this diversity lies in the various souls being distinguished accordingly as the operation of the soul transcends the operation of the corporeal nature in various ways; for the whole corporeal nature is subject to the soul, and is related to it as its matter and instrument. There exists, therefore, an operation of the soul which so far exceeds the corporeal nature that it is not even performed by any corporeal organ; and such is the operation of the "rational soul." Below this, there is another operation of the soul, which is indeed performed through a corporeal organ, but not through a corporeal quality, and this is the operation of the "sensitive soul"; for though hot and cold, wet and dry, and other such corporeal qualities are required for the work of the senses, yet they are not required in such a way that the operation of the senses takes place by virtue of such qualities; but only for the proper disposition of the organ. The lowest of the operations of the soul is that which is performed by a corporeal organ, and by virtue of a corporeal quality. Yet this transcends the operation of the corporeal nature; because the movements of bodies are caused by an extrinsic principle, while these operations are from an intrinsic principle; for this is common to all the operations of the soul; since every animate thing, in some way, moves itself. Such is the operation of the "vegetative soul"; for digestion, and what follows, is caused instrumentally by the action of heat, as the Philosopher says (De Anima ii, 4).

Now the powers of the soul are distinguished generically by their objects. For the higher a power is, the more universal is the object to which it extends, as we have said above (Question [77], Article [3], ad 4). But the object of the soul's operation may be considered in a triple order. For in the soul there is a power the object of which is only the body that is united to that soul; the powers of this genus are called "vegetative" for the vegetative power acts only on the body to which the soul is united. There is another genus in the powers of the soul, which genus regards a more universal object---namely, every sensible body, not only the body to which the soul is united. And there is yet another genus in the powers of the soul, which genus regards a still more universal object---namely, not only the sensible body, but all being in universal. Wherefore it is evident that the latter two genera of the soul's powers have an operation in regard not merely to that which is united to them, but also to something extrinsic. Now, since whatever operates must in some way be united to the object about which it operates, it follows of necessity that this something extrinsic, which is the object of the soul's operation, must be related to the soul in a twofold manner. First, inasmuch as this something extrinsic has a natural aptitude to be united to the soul, and to be by its likeness in the soul. In this way there are two kinds of powers ---namely, the "sensitive" in regard to the less common object---the sensible body; and the "intellectual," in regard to the most common object---universal being. Secondly, forasmuch as the soul itself has an inclination and tendency to the something extrinsic. And in this way there are again two kinds of powers in the soul: one---the "appetitive"---in respect of which the soul is referred to something extrinsic as to an end, which is first in the intention; the other---the "locomotive" power---in respect of which the soul is referred to something extrinsic as to the term of its operation and movement; for every animal is moved for the purpose of realizing its desires and intentions.

The modes of living are distinguished according to the degrees of living things. There are some living things in which there exists only vegetative power, as the plants. There are others in which with the vegetative there exists also the sensitive, but not the locomotive power; such as immovable animals, as shellfish. There are others which besides this have locomotive powers, as perfect animals, which require many things for their life, and consequently movement to seek necessaries of life from a distance. And there are some living things which with these have intellectual power---namely, men. But the appetitive power does not constitute a degree of living things; because wherever there is sense there is also appetite (De Anima ii, 3).

Thus the first two objectives are hereby solved.

3. The "natural appetite" is that inclination which each thing has, of its own nature, for something; wherefore by its natural appetite each power desires something suitable to itself. But the "animal appetite" results from the form apprehended; this sort of appetite requires a special power of the soul---mere apprehension does not suffice. For a thing is desired as it exists in its own nature, whereas in the apprehensive power it exists not according to its own nature, but according to its likeness. Whence it is clear that sight desires naturally a visible object for the purpose of its act only---namely, for the purpose of seeing; but the animal by the appetitive power desires the thing seen, not merely for the purpose of seeing it, but also for other purposes. But if the soul did not require things perceived by the senses, except on account of the actions of the senses, that is, for the purpose of sensing them; there would be no need for a special genus of appetitive powers, since the natural appetite of the powers would suffice.

4. Although sense and appetite are principles of movement in perfect animals, yet sense and appetite, as such, are not sufficient to cause movement, unless another power be added to them; for immovable animals have sense and appetite, and yet they have not the power of motion. Now this motive power is not only in the appetite and sense as commanding the movement, but also in the parts of the body, to make them obey the appetite of the soul which moves them. Of this we have a sign in the fact that when the members are deprived of their natural disposition, they do not move in obedience to the appetite.

Article: 2 Whether the parts of the vegetative soul are fittingly described as the nutritive, augmentative, and generative?

Objection: 1. It would seem that the parts of the vegetative soul are not fittingly described---namely, the nutritive, augmentative, and generative. For these are called "natural" forces. But the powers of the soul are above the natural forces. Therefore we should not class the above forces as powers of the soul.

2. Further, we should not assign a particular power of the soul to that which is common to living and non-living things. But generation is common to all things that can be generated and corrupted, whether living or not living. Therefore the generative force should not be classed as a power of the soul.

3. Further, the soul is more powerful than the body. But the body by the same force gives species and quantity; much more, therefore, does the soul. Therefore the augmentative power of the soul is not distinct from the generative power.

4. Further, everything is preserved in being by that whereby it exists. But the generative power is that whereby a living thing exists. Therefore by the same power the living thing is preserved. Now the nutritive force is directed to the preservation of the living thing (De Anima ii, 4), being "a power which is capable of preserving whatever receives it." Therefore we should not distinguish the nutritive power from the generative.

On the contrary The Philosopher says (De Anima ii, 2,4) that the operations of this soul are "generation, the use of food," and (cf. De Anima iii, 9) "growth."

I answer that The vegetative part has three powers. For the vegetative part, as we have said (Article [1]), has for its object the body itself, living by the soul; for which body a triple operation of the soul is required. One is whereby it acquires existence, and to this is directed the "generative" power. Another is whereby the living body acquires its due quantity; to this is directed the "augmentative" power. Another is whereby the body of a living thing is preserved in its existence and in its due quantity; to this is directed the "nutritive" power.

We must, however, observe a difference among these powers. The nutritive and the augmentative have their effect where they exist, since the body itself united to the soul grows and is preserved by the augmentative and nutritive powers which exist in one and the same soul. But the generative power has its effect, not in one and the same body but in another; for a thing cannot generate itself. Therefore the generative power, in a way, approaches to the dignity of the sensitive soul, which has an operation extending to extrinsic things, although in a more excellent and more universal manner; for that which is highest in an inferior nature approaches to that which is lowest in the higher nature, as is made clear by Dionysius (Div. Nom. vii). Therefore, of these three powers, the generative has the greater finality, nobility, and perfection, as the Philosopher says (De Anima ii, 4), for it belongs to a thing which is already perfect to "produce another like unto itself." And the generative power is served by the augmentative and nutritive powers; and the augmentative power by the nutritive.

Reply to Objection: 1. Such forces are called natural, both because they produce an effect like that of nature, which also gives existence, quantity and preservation (although the above forces accomplish these things in a more perfect way); and because those forces perform their actions instrumentally, through the active and passive qualities, which are the principles of natural actions.

2. Generation of inanimate things is entirely from an extrinsic source; whereas the generation of living things is in a higher way, through something in the living thing itself, which is the semen containing the principle productive of the body. Therefore there must be in the living thing a power that prepares this semen; and this is the generative power.

3. Since the generation of living things is from a semen, it is necessary that in the beginning an animal of small size be generated. For this reason it must have a power in the soul, whereby it is brought to its appropriate size. But the inanimate body is generated from determinate matter by an extrinsic agent; therefore it receives at once its nature and its quantity, according to the condition of the matter.

4. As we have said above (Article [1]), the operation of the vegetative principle is performed by means of heat, the property of which is to consume humidity. Therefore, in order to restore the humidity thus lost, the nutritive power is required, whereby the food is changed into the substance of the body. This is also necessary for the action of the augmentative and generative powers.

Article: 3 Whether the five exterior senses are properly distinguished?

Objection: 1. It would seem inaccurate to distinguish five exterior senses. But there are many kinds of accidents. Therefore, as powers are distinguished by their objects, it seems that the senses are multiplied according to the number of the kinds of accidents.

2. Further, magnitude and shape, and other things which are called "common sensibles," are "not sensibles by accident," but are contradistinguished from them by the Philosopher (De Anima ii, 6). Now the diversity of objects, as such, diversifies the powers. Since, therefore, magnitude and shape are further from color than sound is, it seems that there is much more need for another sensitive power than can grasp magnitude or shape than for that which grasps color or sound.

3. Further, one sense regards one contrariety; as sight regards white and black. But the sense of touch grasps several contraries; such as hot or cold, damp or dry, and suchlike. Therefore it is not a single sense but several. Therefore there are more than five senses.

4. Further, a species is not divided against its genus. But taste is a kind of touch. Therefore it should not be classed as a distinct sense of touch.

On the contrary The Philosopher says (De Anima iii, 1): "There is no other besides the five senses."

I answer that The reason of the distinction and number of the senses has been assigned by some to the organs in which one or other of the elements preponderate, as water, air, or the like. By others it has been assigned to the medium, which is either in conjunction or extrinsic and is either water or air, or such like. Others have ascribed it to the various natures of the sensible qualities, according as such quality belongs to a simple body or results from complexity. But none of these explanations is apt. For the powers are not for the organs, but the organs for the powers; wherefore there are not various powers for the reason that there are various organs; on the contrary, for this has nature provided a variety of organs, that they might be adapted to various powers. In the same way nature provided various mediums for the various senses, according to the convenience of the acts of the powers. And to be cognizant of the natures of sensible qualities does not pertain to the senses, but to the intellect.

The reason of the number and distinction of the exterior senses must therefore be ascribed to that which belongs to the senses properly and "per se." Now, sense is a passive power, and is naturally immuted by the exterior sensible. Wherefore the exterior cause of such immutation is what is "per se" perceived by the sense, and according to the diversity of that exterior cause are the sensitive powers diversified.

Now, immutation is of two kinds, one natural, the other spiritual. Natural immutation takes place by the form of the immuter being received according to its natural existence, into the thing immuted, as heat is received into the thing heated. Whereas spiritual immutation takes place by the form of the immuter being received, according to a spiritual mode of existence, into the thing immuted, as the form of color is received into the pupil which does not thereby become colored. Now, for the operation of the senses, a spiritual immutation is required, whereby an intention of the sensible form is effected in the sensile organ. Otherwise, if a natural immutation alone sufficed for the sense's action, all natural bodies would feel when they undergo alteration.

But in some senses we find spiritual immutation only, as in "sight" while in others we find not only spiritual but also a natural immutation; either on the part of the object only, or likewise on the part of the organ. On the part of the object we find natural immutation, as to place, in sound which is the object of "hearing"; for sound is caused by percussion and commotion of air: and we find natural immutation by alteration, in odor which is the object of "smelling"; for in order to exhale an odor, a body must be in a measure affected by heat. On the part of an organ, natural immutation takes place in "touch" and "taste"; for the hand that touches something hot becomes hot, while the tongue is moistened by the humidity of the flavored morsel. But the organs of smelling and hearing are not affected in their respective operations by any natural immutation unless indirectly.

Now, the sight, which is without natural immutation either in its organ or in its object, is the most spiritual, the most perfect, and the most universal of all the senses. After this comes the hearing and then the smell, which require a natural immutation on the part of the object; while local motion is more perfect than, and naturally prior to, the motion of alteration, as the Philosopher proves (Phys. viii, 7). Touch and taste are the most material of all: of the distinction of which we shall speak later on (ad 3,4). Hence it is that the three other senses are not exercised through a medium united to them, to obviate any natural immutation in their organ; as happens as regards these two senses.

Reply to Objection: 1. Not every accident has in itself a power of immutation but only qualities of the third species, which are the principles of alteration: therefore only suchlike qualities are the objects of the senses; because "the senses are affected by the same things whereby inanimate bodies are affected," as stated in Phys. vii, 2.

2. Size, shape, and the like, which are called "common sensibles," are midway between "accidental sensibles" and "proper sensibles," which are the objects of the senses. For the proper sensibles first, and of their very nature, affect the senses; since they are qualities that cause alteration. But the common sensibles are all reducible to quantity. As to size and number, it is clear that they are species of quantity. Shape is a quality about quantity. Shape is a quality about quantity, since the notion of shape consists of fixing the bounds of magnitude. Movement and rest are sensed according as the subject is affected in one or more ways in the magnitude of the subject or of its local distance, as in the movement of growth or of locomotion, or again, according as it is affected in some sensible qualities, as in the movement of alteration; and thus to sense movement and rest is, in a way, to sense one thing and many. Now quantity is the proximate subject of the qualities that cause alteration, as surface is of color. Therefore the common sensibles do not move the senses first and of their own nature, but by reason of the sensible quality; as the surface by reason of color. Yet they are not accidental sensibles, for they produce a certain variety in the immutation of the senses. For sense is immuted differently by a large and by a small surface: since whiteness itself is said to be great or small, and therefore it is divided according to its proper subject.

3. As the Philosopher seems to say (De Anima ii, 11), the sense of touch is generically one, but is divided into several specific senses, and for this reason it extends to various contrarieties; which senses, however, are not separate from one another in their organ, but are spread throughout the whole body, so that their distinction is not evident. But taste, which perceives the sweet and the bitter, accompanies touch in the tongue, but not in the whole body; so it is easily distinguished from touch. We might also say that all those contrarieties agree, each in some proximate genus, and all in a common genus, which is the common and formal object of touch. Such common genus is, however, unnamed, just as the proximate genus of hot and cold is unnamed.

4. The sense of taste, according to a saying of the Philosopher (De Anima ii, 9), is a kind of touch existing in the tongue only. It is not distinct from touch in general, but only from the species of touch distributed in the body. But if touch is one sense only, on account of the common formality of its object: we must say that taste is distinguished from touch by reason of a different formality of immutation. For touch involves a natural, and not only a spiritual, immutation in its organ, by reason of the quality which is its proper object. But the organ of taste is not necessarily immuted by a natural immutation by reason of the quality which is its proper object, so that the tongue itself becomes sweet and bitter: but by reason of a quality which is a preamble to, and on which is based, the flavor, which quality is moisture, the object of touch.

Summa Th. I EN Qu.77 a.6