Chapter 14

Different natural agents, and their different way of operating.
First, the action attributed to bodies

1239. All that has been said was, I believe, necessary as a preface to the explanation of movement in the rational principle. The condition proper to this movement is not clear conceptually unless 1. we understand the nature of movement in general of all entia, especially of entia which are subjects of transient acts; and 2. we compare the movement of the rational principle with that according to which other agents in nature move. We have already dealt with the first point in the preceding chapter; we shall now deal with the second.

1240. The only full space (that is, a distinct space given by means of the body which expands in it) presented to human beings through nature, is that of the fundamental feeling. The limits of this space, which are not felt initially, are found by means of surface sensations. These limits could not be perceived unless we felt some space beyond them.(130)
Here we must pause for a moment. What has been said already needs some explanation if we are to make headway. - How can we feel something beyond our body?

1241. Although we truly perceive unlimited space, this space is indistinct. In other words, it has no relationship for the moment with the bodies which either fill it or can fill it. This space is not sufficient, therefore, to explain how we acquire knowledge of distinct space which exceeds the limits of our body, that is, of the relationship between our body and immense space.

The solution to this difficulty must be found in the distinction between the two ways of feeling, subjective and extrasubjective.
The subject spreads itself as proprietor in the corporeal fundamental feeling where it is at home as though it were a part of itself, a continuation of itself. The subject acts in it and needs it as an essential condition of itself. No linear or surface limits are manifest here. We are dealing with a solid feeling, outside of which nothing corporeal is felt, nothing can be felt; there are no sensible relationships with any foreign body.

Extrasubjective sensation, however, is of a totally different nature. It betrays the presence of a force foreign to that of the felt element. This force acts energetically (although sometimes pleasantly) on the fundamental feeling. The foreign force acts in the extension itself of feeling, in the fundamental felt element, which is then outlined and shaped. It is necessary to understand carefully the nature of these surface limits which our fundamental felt element thus acquires.

First, when our touch is affected by a foreign body, we realise that this body is foreign because we feel its action is not that of the sentient principle. Rather, the foreign body is in the action of the sentient principle in the sense that we feel not the foreign agent in itself, but only the effect and term of its action, because we feel a surface, not a solid. We feel the term of the action, therefore, but not the foreign body. This is quite different from what occurs in the fundamental felt element, which is not felt as a surface term of action but is the agent in the whole of the solid space in which it expands as agent. The term of the foreign action is, therefore, in our fundamental felt element which receives this action. Consequently, the sensible surface which is the term of the foreign action is perceived as limit to the fundamental feeling. This surface is thus distinguished from the remaining part of the fundamental feeling, and becomes the term of two agents, the foreign agent and its own agent which is the fundamental felt element (in so far as it is sensiferous).

This all happens through touch which is the proper measure of bodies (we prescind for the moment from sight and the other senses).(131) Consequently, if our body were immobile we would be unable to know simultaneously with our touch the surface of a foreign body larger than the surface of our own body, which serves to measure the surface of the foreign body.

If therefore we want to explain how we can perceive a body larger than our own we have to take cognisance of the movement of exterior bodies and our own body. Let us take the movement of exterior bodies first. If different bodies act successively on the same part of our body, these bodies are either perfectly equal in extension, form, etc., or are different. If they are perfectly equal and applied successively to the same part of our body, we will be unable to distinguish whether the agent is one and the same body, the same power operating with repeated acts, or several bodies (if we rely on touch only without the help of other senses). But if the bodies vary in extension and shape we will take them for different bodies. This happens not in virtue of the sentient principle alone and of the retentive faculty proper to it (I prescind from this for the moment because there is no need to consider such a subtle question), but through our rational retentive faculty. By comparing one sensible, sensiferous surface with another, we find that they differ. Thus we have in our spirit information about several surfaces.

For example, we may have ten surfaces each of six square centimetres, but varying in shape. This alone is sufficient for us to begin to conceive an extension greater than the corresponding extension in our body. In fact, the surface, in so far as it pertains to our fundamental feeling, cannot ever be multiplied. We always feel it as the same. A single surface of six square centimetres of our body is the field, as it were, where we can feel six square centimetres of extension in the exterior force. This measurement can be multiplied as often as we wish, according to the number of sensations of different shape which are repeated and multiplied successively.

1242. We come now to the movement of our body. It is certain that by moving our body and constantly receiving new and different sensations from bodies around us which differ in figure and activity, we can by means of our rational retentive faculty acquire information of indefinitely extended space. This space has no assignable limit. But the difficulty lies in explaining the movement of our body. We said that the feeling and rational principles are immovable relative to local motion. How, then, can we move our subjective body? What is this movement?

We need to consider that we perceive our body in two ways, extrasubjectively and subjectively. We feel our body extrasubjectively as we feel every other body, that is, in so far as it too has sensiferous power which makes it visible, touchable, etc. Subjectively, our body is the felt element of the fundamental feeling. But our extrasubjective body does not form part of the fundamental feeling. Indeed, its sensiferous power is foreign to and in opposition to the fundamental feeling. Let us imagine, therefore, that we have perceived our body only subjectively, not extrasubjectively. In this case, our body no longer has motion. In fact, I have already shown in my treatise on ideas that our motion is not sensible.(132) But if our fundamental feeling feels no motion, motion does not enter it. Our fundamental feeling is essentially feeling, and only what is sensible enters feeling.

It may be objected that when we ourselves move our body, for example, by walking or jumping, we feel the effort that we make in moving. This is true, but the effort that we make to move is not motion, but its cause. Motion, by which we pass from place to place, does not therefore enter the fundamental feeling, although the force and cause of motion are found there.
The motion of passage is only a change made outside the subject, a change in our extrasubjective body, a mutation in the sensiferous force. But it is not present in any way in the fundamental feeling, which remains immobile.

1243. Nevertheless, the extrasubjective body moves in such a way that we notice, through extrasubjective experience, that it has changed place. We realise this by means of its different relationship with surrounding bodies. At these moments, our fundamental feeling, and hence our subjective body, is still present to the extrasubjective phenomena given by our moved body. Our subjective body has not changed its relationship with our extrasubjective body. If our extrasubjective body now occupies a different space, we normally say that our subjective body also occupies this other space. The subjective body, it would seem, has been transported, has been moved.

Aristotle was led by this observation to posit in the soul the kind of movement which he describes as per accidens. He likens it to the motion of colour which moves not as colour, but as adhering to a body which moves. But this, as we said, is an error. Going back to the fundamental felt element, we see clearly that motion must either be felt and thus enter into feeling itself, or not be motion proper to feeling, which is closed in itself by its very essence so that change of things outside it is not movement springing from itself. We have to say, therefore, that local movement is an entirely extrasubjective phenomenon, that is, a phenomenon revealed only through extrasubjective experience. It is not some subjective phenomenon experienced either as an accident of the subject itself or of its fundamental felt element. Now, extrasubjective phenomena are produced by the sensiferous force. We can say, therefore, that the relationship between our fundamental feeling and the sensiferous force scattered throughout nature — for example, in external bodies — changes with the movement of our own body. But feeling itself does not change or move.

1244. We come now to a series of objections.
The surfaces of the fundamental feeling itself are felt in the fundamental feeling through the action of the sensiferous element. These surfaces move. — I answer: 1. Surfaces are felt when the sensiferous force is actually applied to our body, but there is no local movement of the surfaces during this action; 2. when the sensiferous force no longer acts on our touch, and our body has been moved from one place to another, the change consists only in a change of relationship between the sensiferous force and our fundamental feeling, as I said.

1245. But our body is seen when it is moved. — I answer: sight experience is totally extrasubjective. What we see is our body in so far as it lies within extrasubjective experience. I have already noted that motion is present in the body considered extrasubjectively. Such a body, however, is totally different from the fundamental felt element.

1246. But surely we feel motion on the surface of our body whenever a particular sensation moves from one point to another of that surface? — I answer: This moving sensation is produced by sensiferous power and hence pertains to the body perceived as extrasubjective. Motion is present in this order of perceptions.

1247. But you have distinguished a simple sentient principle and an extended term in the fundamental-animal feeling. In addition, you have acknowledged the condition of the felt element and of the sensiferous element in the extended term. Even granted that motion is not proper to the sentient principle, which is simple and incorporeal, it must be granted to the extended term for two reasons: 1. because the extended term is extended, and something extended can be moved from one place to another; 2. because the sensiferous element, in which, as you agree, motion is present, is in that same extended element.

I answer: The term of the fundamental feeling purely as sensiferous power in itself is not the term of the fundamental feeling. Rather, it is the power capable of changing the term of the fundamental feeling, that is, of constituting it in a way other than what it actually is. Let me explain. The fundamental felt element, simply as felt, is in the sentient principle. As we have seen, it is present in the way that the extended element is present in the sentient principle, that is, as contained in container. Moreover, there is such a perfect union between sentient principle and extended element that they form a single feeling. It is different for the sensiferous force which is not in the sentient principle in this way. This force simply acts in the extended term of feeling and changes it. Consequently, the sentient principle is neither united stably with the sensiferous force, nor receives the force's action directly. It receives this action indirectly because the felt element of the sentient principle is changed by a force which is not its own. Moreover, when the sensiferous force actually acts in the extended element, in the term of feeling, it does not present in itself any movement from place to place, but simply action in the felt element itself, the term of the sentient element.

The second of these two objections is this: The felt element, because it is in the extended fundamental feeling, is capable of moving. I answer: not every extended element is capable of motion. As we saw, infinite space itself, which is essentially immobile, is not suitable for motion. If there is to be some possibility of movement, some other space must be present besides the space occupied by the extended element, into which this element can be transported. But we have seen that the proper extended element of the fundamental felt element has no boundaries; only when surface boundaries are perceived is it necessary, in order to perceive them, to perceive some other space beyond them. The fundamental felt element is, on the contrary, of such a nature that beyond it, beyond its felt element, no other extension is perceived.

All extension finishes in the fundamental extended element with the result that it is impossible for it to be subject to some movement of its own; there is no other space in which it can place itself except that which it occupies. In order to conceive some change of place, it is necessary to go outside this felt element and enter the extrasubjective world. But when we come to know the phenomena of this extrasubjective world, it seems to us that the fundamental extended element moves. This motion, however, consists, as we have said, only in a change of relationship between the felt extended element of the fundamental feeling and the extrasubjective world. This relationship is not a relationship of place to place, of extended element to extended element, but of extended element to feeling. The change takes place, therefore, in an unextended relationship of sensility and, properly speaking, in a relationship between the cause, the agent in feeling (the sensiferous element) and feeling itself. Movement, on the contrary, is a change in relationship between extended element and extended element.

1248. Another objection. If the whole fundamental felt element has no motion, if it is not transported from place to place, you have at least to admit that the extended element of the fundamental feeling can be increased and diminished. But this implies a kind of movement either through extension or restriction. — My answer is this. Although the fundamental felt element can be increased and diminished, this happens through naturation. not through motion. The felt element begins to be in a greater extension, or ceases to be in a part of it. This, however, is not local motion, but a kind of creation or cessation of a new felt-extended part.

1249. Another objection. The fundamental feeling is not uniform. If some part of it is felt more than another, or in a different way, it will be able to move from place to place within a fundamental felt extended element. — My answer is this. What you have described can perhaps be called movement, but it is the only movement that can be admitted in the fundamental feeling. We have to explain it, however, and in explaining it we realise that it is not true movement because it prescinds from every action of the sensiferous element which can be mingled in it. In fact, we have already seen that if the corporeal particles in which the fundamental feeling terminates are moved without losing their continuity, the feeling is stimulated, that is, gains greater, different vivacity.

But when we speak about movement of corporeal particles, we are speaking first of all about an extrasubjective phenomenon.
The subjective phenomenon corresponding to this is the greater vivacity and variety in feeling which we have mentioned. The question, therefore, consists in knowing if this change in the subjective phenomenon can be called motion.

But

1. The movement of each particle is not sensible, as we have seen, because the movement of the felt element does not take place in the felt element, and is therefore totally extrasubjective;

2. the movement of two or more particles which move without losing continuity does not produce any other change in the felt element, as far as extension is concerned, except for increase on one hand and diminution on the other. But this is not movement, as we have seen again; finally,

3. if the particles constitute an organ and the intestine movements of the particles succeed one another so that the particles in the first line move before those in the second, and so on, we have a succession of motions which must have a succession of stimuli distributed in the various parts of the organ. The stimulated movement then produces the phenomenon of internal movement because the same sensation appears to pass from one extreme to the other of the organ, which is felt in its totality through the feeling of continuity.

This is the only movement which can be conceived in the fundamental felt element. But granted the animal retentive faculty, which preserves the trace of the preceding sensation, and even more the rational retentive faculty which preserves the memory of already experienced sensations and compares them, this movement is subjective. Nevertheless we should remember that no sensation is numerically the same. When one sensation ceases another takes its place so that it appears as a series of sensations representing a movement, just as the image in the mirror moves although no identical body is transferred from place to place in the mirror.(133) Here we are dealing with phenomenal movement, that is, movement residing in feeling. Consequently, there is nothing contradictory in its having a kind of continuity in so far as the felt element is continuous and the new sensation can begin where the former sensation finishes, or can mix the extremes of these sensations.

1250. Relative to the sentient principle, therefore, that is, to the sensitive soul, we have shown that it is immune from any movement whatsoever.
But while we deny local motion to the fundamental felt element, as we have said, and to the sentient principle, this is not to be taken in the sense that we predicate rest about these things. Rest can be assigned only to that in which motion can be present. Rest is relative to motion. We should say, therefore, that the fundamental felt element and the sentient principle have neither motion nor rest. This is similar to situations where there is no extension. No extension means no point, which is the term of extension.

1251. From all these things we can conclude:

1. Space, because it is without second, transient acts, needs no explanation relative to its way of action.

2. Body presents two activities, what is felt and the sensiferous.

3. Properly speaking, the felt element has no local motion; its action depends upon its being given to the sentient element and, as it were, posited in it. This kind of action can come originally only from the Creator, the Maker of feeling. As I said elsewhere, the animated being is not formed, but posited in nature.(134)

4. Only the action of the sensiferous element, the cause of movement, now needs to be explained. This action depends for its cause on the corporeal principle which, however, does not fall within our experience. We cannot, therefore, indicate how it acts with second acts, whether they are immanent or transient.

1252. Knowing only that movement and consequently the endeavour to move,(135) that is, the corporeal force, depends on the sensitive principle and an unknown agent is sufficient to conclude that the body does not pass to its transient acts alone. It receives motion and force from the sensitive principle as it receives existence from the corporeal principle, which itself can be a principle of motion, although the way in which it produces this motion may be altogether hidden.

1253. Force is considered as an immanent act in bodies; motion as a transient act. It will help, therefore, if we indicate the relationship between this corporeal force and motion.
We said that the extended-felt element does not contain the cause of extrasubjective movement. If it did, this cause, now become the extended-felt element, has lost the nature of force, dominated as it is by the sentient principle. We now have to consider this force as distinct from the felt element; we have to determine it from its effects, which are:

1254. 1. Communication of motion. — When one body strikes another, the body which is struck and free moves in the same direction as the body which strikes it. This effect is reduced to impenetrability and to inertia. Because one body cannot penetrate another and motion has to be preserved through inertia, one gives way to another with a velocity in direct proportion to the quantity of motion in the body which strikes and in indirect proportion to the mass of the body which is struck. This fact is relative to the communication of already existing motion, not to the beginning of motion.

2. The conservation of motion. — A body in motion continues through inertia to move in the same direction. This effect supposes that the cause of the motion persists. This cause cannot be the body itself because it is indifferent to rest and to motion. It must be, therefore, an incorporeal force which, different from the body, acts in the body.

3. Attraction. — This incorporeal force is simply an endeavour to move, a permanent endeavour, on the part of one body towards another. The permanence of this endeavour indicates a cause of motion different in its activity from the cause of the conservation of motion. The fact behind the cause which conserves motion is this. Two bodies of equal mass move with equal speed towards one another in the same line. When they strike, motion is destroyed. They become stationary so that the same quantity of motion remains in the same direction. The two bodies now at rest are in contact with one another. The endeavour to move in the directions which they previously held is no longer present. They no longer bear down upon one another. On the contrary, the cause of attraction produces pressure in them by which they tend to penetrate one another.

Experience shows, therefore, that three causes of motion concur in the nature of motion:
1. A cause that simply produces motion, that is, which makes a body pass from rest to motion, and vice-versa.
2. A cause that governs conservation and the communication of motion between one body and another.
3. The cause that produces a constant endeavour of one body to move towards another (that is, phenomena of attraction).

1255. As far as I can see, the first and third causes are sufficiently explained by the movement-activity of the sentient principle joined with elements of matter and by the laws according to which that activity operates.

1256. The second supposes another principle foreign to bodies. This principle constitutes bodies and in constituting them imposes laws of inertia.
According to these laws, motion in one direction is annihilated by the same kind of motion in the opposite direction. The endeavour that bodies possess to penetrate one another ceases in this case with the cessation of movement because it arises from movement and not from the force which causes it. This force has ceased. All the laws of conservation and communication of motion are consequences of this first law.
The force which produces motion remains even after the production of motion. If this cause is connected with bodies, as in attraction, the endeavour that bodies make to penetrate one another does not cease with the cessation of movement because it is not produced by movement, itself an effect of the force, which does not change its own nature of force.

1257. Motion is renewed at every single moment in the conservation of simple motion, but no new endeavour is added to that which arises from motion itself. Consequently, motion is uniform.

1258. The renewal of the endeavour towards motion at every moment is an effect of attraction. The endeavour produces new motion, while the body is already moving as a consequence of conservation of preceding motion. The result is accelerated motion dependent upon the square of the brief intervals. Accelerated motion, therefore, is made up of two principles: 1. the principle of the production of motion and 2. the principle of its conservation.

1259. Impenetrability, although destroying motion and the endeavour proceeding from motion, does not destroy the constant endeavour which precedes motion and causes its production. If two equal bodies move in opposite directions with equal motion but without attraction, all their motion, together with the free endeavour which comes from motion (always an instantaneous endeavour) ceases when they come into contact. In other words, it ceases during the brief interval which is necessary to extinguish motion. On the other hand, if two bodies draw close as a result of attraction, all their motion ceases when they make contact (granted that their mass is equal) although it has increased according to the square of the brief intervals during which the bodies have moved towards one another. Nevertheless, there is no cessation of the constant endeavour with which they tend to penetrate one another or at least (and this seems to me closer to the truth) to touch one another at all their points, to centre themselves.

1260. It is clear that two powers are at work in bodies: 1. a constant cause of already produced motion; 2. a constant cause of endeavour to produce motion.

1261. We said that the cause of motion is certainly distinct from bodies because motion is excluded from the essence of bodies. Can the same be said about the cause of the endeavour to move?

We have to say that the cause of this endeavour, which is also called attraction or living force, must act incessantly in bodies because all bodies attract one another (I leave aside so-called weightless bodies concerning which the question is still open). But it is easy to show that this endeavour does not form part of the essence of bodies. We simply need to consider that each body has its own essence in itself; it finishes in itself; nothing outside of it pertains to it.

Attraction, however, is directed by the relationship of one body with another. Necessarily, therefore, the cause of attraction is not a body, but an agent capable of embracing the relationship between several bodies. This seems to confirm once more the opinion that such power may be a sentient principle united with all corporeal atoms. This opinion would, in fact, remove the difficulty. Moreover, because experience proves that the sentient principle can be a cause of motion, the hypothesis, if it is such, possesses the two conditions required by Newton: it is something existing in nature and has sufficient power to produce its effect.

However, we have certainly demonstrated that matter is per se inert and needs to receive motion. In itself it has no faculty for producing motion.

Notes

(130) AMS , 154-155.

(131) NE , vol. 2, 922-924.

(132) NE , vol. 2, 806.

(133) A body is said to be identical even if successively in different places because place does not form part of the essence or substance of body. But the sense-experience which is aroused in different parts of the fundamental felt element cannot be called identical as a result of the relationship the experience has essentially with the felt element of which it forms a part. One part of the felt element is not identical with another.

(134) AMS , 323-325.

(135) The endeavour to move, or the living force, would seem a fact from which the continuity of movement could be inferred. Careful consideration, however, does not necessarily lead to any conclusion about the existence of continuous motion. First, we have to admit impenetrability , an undeniable quality of bodies. Impenetrability limits the force which produces motion in bodies in so far as it impedes this force from producing the effect called motion. But the force (the sentient principle, let us say) can nevertheless continue to operate according to its laws. The result is an endeavour to move, although not to continuous motion. Let us imagine that one body is weighing down another. If the first body wishes to penetrate a millimetre into the place occupied by the second, contiguous body, it will press down upon it and, if it has the strength, will even force it to move over. In other words, the body cedes its place to the stronger body so as not to be penetrated. We would, therefore, have to know the laws according to which this force operates in order to gain an adequate explanation of the laws which govern the movement of bodies.