CHAPTER 7

Origin of the idea of movement

800. One of the great actions carried out successively that form and measure time(153) is movement, which we now have to examine.
Relative to us, movement is active and passive.
I call it active when we ourselves cause it by using in any way the locomotive faculty with which we are endowed. Thus we may walk or otherwise dispose the position of our body.
Movement is passive when it is produced by an exterior force causing our body to change place.

801. Besides our own movement, there is also movement in bodies surrounding us, which however we experience neither actively nor passively.

802. Because movement is something affecting both our own and external bodies, we perceive it along with our perception of bodies in a kind of co-perception. Hence, we apprehend it in as many ways as there are perceptions of bodies. As we have seen, we perceive bodies in three ways:

1. Subjectively, through the fundamental feeling. This applies to active movement, where consciousness indicates that we are its cause.

2. Subjectively once more, through acquired sensations which cause us to feel movement in the parts of our affected sensitive organs; in this way we perceive subjectively some kind of passive movement.

3. Extrasubjectively, through the senses which, in enabling us to perceive our own and external bodies, also make us perceive the movements, active or passive relative to us, taking place in all bodies. These variations of activity or passivity of movement can be distinguished and perceived only subjectively, not extrasubjectively.

Strictly speaking, I should confine my attention to the subjective ways of perceiving movement because so far I have only dealt with subjective, not extrasubjective ways of perceiving bodies. This, however, would leave our work very lop-sided, and I think it better consequently not to separate totally the extrasubjective from the subjective way of perceiving the movement of bodies.

803. I have no wish to go too deeply into an examination of the nature of movement. My sole aim is to indicate the origin of the ideas of movement.
Here, too, observation and especially the facts presented to us by consciousness must be our guide.
I shall speak first about active then about passive movement.
We have the faculty to move our body.(154) What is this faculty? What does observation tells us about it?

The fundamental feeling causing us to perceive our body directly is furnished with a mode we call extension.
The faculty for moving our body as presented to us directly through observation is a power of our spirit over the fundamental feeling consisting in a faculty for changing the mode of the feeling in a given way.
The new mode taken by the feeling is a new space in which it is diffused, enabling us to say that changing the mode of the fundamental feeling indicates a change of space or place.
Because the soul has the power to change the mode of the fundamental feeling, it is also said to have power of movement over its own body.
In fact, if the body is the agent producing in the soul the fundamental feeling which has extension as its term, the soul must be acting on the agent if facts show that it can change its action in a given way.

804. Not only do we possess the energy to move ourselves; we can also be moved.
When we move ourselves, the quantity of effort we make gives us some perception of movement and a way of measuring it.
When we are moved by some external force, however, we do not always perceive our movement.
If the force moving us produces change in our sensitive organs - for example, when we are pushed or dragged from one place to another - we experience an action upon us and perceive our movement. This movement, however, is not seconded by the other inert parts of our body outside the immediate effect of the moving force. If we are moved by an external force making us change the position of the whole of our body simultaneously, the force changes nothing in the body because it does not disturb any individual particle relative to the whole body. In this case, our interior feeling provides no perception of the quantity of movement, or of the movement itself.

This explains why we have no perception of the movement with which we are involved by living on a planet revolving on its axis at a speed of thousands of miles an hour. We are not aware of being moved because we do not move ourselves, but depend upon a uniform force without experiencing any internal or external sensation in our vision or touch, or in any other senses indicating our movement.

805. While our active movement is perceived in two ways, through the interior feeling of consciousness and our external sensations, our passive movement is perceived through external sensations alone.

806. A corollary of this observation is that our movement is not per se sensible.
Observation shows that we can be moved, and not feel movement in any way.
As we have said, we know movement subjectively through its cause, and extrasubjectively through its effects, but if our position is changed not by ourselves but through an external force producing no change in our sensitive organs we cannot know this movement because there is no change in our feeling [App., no. 28].

807. It is true that when a movement of any sort is produced in our sensitive organs, we feel the sensitive particles composing those organs in a shape different from that to which we previously referred the fundamental feeling. Consequently, the feeling itself is moved and heightened in such a way that, along with its modification, we perceive a movement in so far as the matter which is felt stimulates our fundamental feeling by changing its form.Nevertheless, the movement is not felt through itself but through the particular circumstance by which it changes the state of the sensitive organ that is always felt by us in its actual state.

Such movement, therefore, is change of the respective position of the molecules composing the sensitive organ that is felt by us according to a law determining the position of the molecules making up the organ. If the position required for one state of the organ (relative to feeling) is altered, the organ takes on another sensible state, and is felt in a new mode and place according to the nature of the change it has experienced.
The sensitive organ could, therefore, be transported vast distances (and this actually happens relative to the daily motion of the earth) without our feeling movement in any way.
We have to conclude that we feel not the movement of the organ, properly speaking, but its sensible state.

We affirm that the feeling and sensible particles making up the organ give the whole organ another form when they are compressed or separated in different ways, proportions and relative positions. In this new form the organ is felt in another way, with varying pleasure or pain, while the change itself is also felt. The new pleasure or pain, that is, the new sensation, is referred to all the sensible points within the new form where the force has acted. Because the previous form was different, the different pleasure or pain with which the organ was felt was referred to different points. We do not feel the change of place undergone by each individual sensitive molecule (the absolute movement of the molecules), but only the change in the total form of the organ, that is, the change of place of several molecules at a time (the relative movement of the molecules), which causes the various parts of the organ to be felt in different places.

808. If we analyse this subjective feeling with which we perceive the sensitive parts of our body when a sensible movement takes place, we see that:

1. this feeling is of variable, corporeal pleasure or pain diffused in an extension of given limits and shape;

2. the shape of this felt extension can change through a relative movement of its parts, and that the feeling is, nevertheless, always diffused, in the extension of all the shapes it assumes;

3. consequently our subjective feeling perceives the particular movement taking place when the shape of the organ changes, but only in that part where the force applied operates in the way necessary to produce a sensation.
Our subjective feeling perceives movement, therefore, in so far as it is a change undergone by its matter.

809. Absolute movement in all its universality is therefore altogether different from sensation.
Relative movement, which takes place in parts of the sensory organ as it changes shape is 'a change in the matter of sensation', and is felt along with the affected matter.

810. Touch perceives the hardness and surface of bodies. But do we perceive movement with touch when the tip of a body, a pencil, for example, is drawn along the length of our stationary arm? At first sight, it seems we do; certainly we perceive something similar to movement.

Nevertheless, we are faced with a difficulty. Although we feel a sensation moving, as it were, along our arm, and through the sensation perceive the body producing it, it would seem that we cannot be sure of the identity of the body producing the sensations. Instead of a single body running along the arm, we could posit a multiplicity of bodies substituting one another in rapid succession and without a noticeable interval [App., no. 29].

811. When we move, what we see around us changes. The changes themselves become signs by which we learn about our own movement and that of others. How this comes about, I shall explain when we deal with the third way of perceiving bodies.
In the meantime, we ask whether we can perceive movement through vision when with motionless eyes we see something which itself moves.
A black dot moving across a white surface gives us the concept of movement, and although we cannot be sure about the movement of the external thing because of the existence of apparent, illusory movements, the concept itself is present to us.

But while the difficulty about the identity of a body relative to sight-sensation is similar to that caused by touch-sensation, it is also less than it. The characteristics of bodies we see are greater in number than those of bodies we touch, so that the union of the former characteristics in different bodies is very difficult. In the case of touch, however, the same sensation can easily be produced by various bodies.

812. In so far as these senses have something in common with touch, perception of movement is the same for them as it is for touch (cf. 810); in so far as they are distinguished from touch by their own special phenomena they do not perceive movement although they can, like all the other senses, measure it by means of time. The time needed for a body to come within range of our touch, sight, smell, taste or hearing is an indication of the length of its movement towards us or our movement towards it.

This measure of movement is possible for those born blind, and for those lacking some, but not all senses.

813. It is a fact that minute extensions escape our observation.
Although the invention of the microscope has revealed a world hidden to observation, nature will always provide subtleties beyond the range of the most developed instruments. The intimate texture of bodies is such as to make me believe that it will always remain veiled to our senses; if an extension is continuously reduced, we must come to a level so minute that it is entirely beyond our advertence.

814. Whatever observation tells us about the continuity of movement, therefore, can only witness to an apparent or phenomenal continuity. Unable to tell us anything about the minute, possible intervals that escape our observation, it cannot provide any certain proof about the real continuity of movement.

815. Although observation fails to provide us with anything certain about the real continuity of movement, we can try to reason about it.
It is true, of course, that reason cannot provide us with facts, but because possibility is the object of the mind alone, it can as such allow us to say something about their possibility or impossibility.
We have already shown that continuity of succession is absurd (cf. 779-799).
But succession is present in movement, as in every action subject to increase and decease.
In movement, therefore, true, real continuity is absurd.
In this way, reason is sometimes able to pass from an argument about mere possibility to conclusions about facts. It can deny them when they are seen to contain an intrinsic repugnance. If this repugnance is absent, however, it cannot affirm their existence; it can only declare them possible.

816. If no true continuity is possible in movement, movement must come about by leaps. But in human thought, leaps have always been excluded from nature.
And indeed a leap in nature is absurd.

817. However, lack of true continuity in movement does not imply the introduction of leaps in nature.
The idea of a leap is not and cannot be present in what occurs in an instant.
A leap supposes two points, and a passage from one to the other without touching what is in between. When we think of passage, on the other hand, we have to include the notion of touching what is between the two points; passing from one place to another without touching what is in between means passing without passing. In this sense, the concept of a leap in nature is absurd because it implies putting links in the middle (the necessary steps) and at the same time mentally jumping over them, an obvious contradiction.

Real movement on the other hand only offers successive existence of a body in several places without our having to think of it as leaping from one to another, provided our imagination does not add anything to the concept of real movement. Such a concept does not imply a leap because it does not entail a necessary passage from one place to the nearest place. Our imagination renders this passage necessary because we are accustomed to the presence of phenomenal continuity of movement in which we think we observe continual passage. But what we see is the simple, successive existence of a body in several places so close together that it is impossible to advert to the distance between them.

We will understand this better if we remember that extension is simply the term of a force, according to our explanation of the concept of force. Force, however, can vary its term and extend itself in one space rather than another without our needing to suppose a true continuous passage between the spaces. It can withdraw itself at immense speed from one place while simultaneously diffusing itself in another. Certainly there is no contradiction in such a concept.

818. I realise that this will be difficult to grasp; our understanding is constantly complicated and confused by the use of our imagination. And it has to be admitted that we have no experience of the fact. The different spaces in which the corporeal force gradually diffuses itself are (according to a law established by the author of nature) so close that separation between them is imperceptible. Hence, our apparent vision of continuity, and our difficulty in thinking that movement could come about in some other way. But let us consider carefully and philosophically the reasoning which leads me to deny perfect, true continuity in local movement.

819. The difficulty present in understanding the truth of what we have said is aggravated by the presence in our mind of the idea of a certain mental continuity of movement, as well as of time.
This abstract, mental continuity consists in the possibility (which we conceive as equal and indifferent) that movement may begin or end in any point whatsoever of time and space.

Because no point of time or space is more apt than another for receiving the beginning or the term of movement, the equal possibility of all points produces, or rather is, the confused idea of abstract continuity in movement of a body between any two moments or points whatever. I call this a 'confused' idea because analysis immediately shows that no continuity can ever be formed by a number of neighbouring points.

(153) Succession in general forms time, but each particular succession is called a measure of time when it is taken as a norm with which to compare other successions.

(154) We could not begin to move any part of our body spontaneously if we lacked the feeling that we could do so. The power that we have over our body, therefore, must be included in the fundamental feeling.

(155) I have distinguished in external sensations: 1. the sensation in the organ; 2. the perception of something different from the organ. I have dealt with movement relative to sensation (cf. 806); I am now speaking about movement relative to corporeal perception.