EXTENSION INSEPARABLE FROM THE IDEA OF BODY.
1. Having seen that among the objects of our sensations, extension alone has any external existence for us as any thing more than a principle of causality, let us now try to understand what extension is.
The idea of extension seems to be inseparable from that of body; at least, I am unable to conceive a body without extension. Take away extension, and the parts disappear, and with them all that has relation with our senses; there is no longer an object, or, if the object remains, it is something altogether different from what is contained in the idea of body. Imagine an apple, for instance, from which you suddenly take away extension. What will remain of it?
I am not now going to examine whether Descartes is right when he says, that the essence of body consists in extension; all that I here assert is that a body cannot be conceived without extension. I do not affirm the identity of two things, but only the inseparability of two ideas in our mind. It is not an opinion, but a fact asserted by consciousness, which is now under discussion.
Abstracting extension, I can conceive, it is true, a substance, or, to speak more generally, a being; but, then,there is no idea of body, unless we confound this idea with, that of substance or of being, in general.
2. All our notions of bodies are obtained through the senses, but without extension no sensation is possible; for without it there can be no color, no sound, no touch, no smell, and no taste; therefore, without extension there remains only something of which we have no idea, a vague notion which cannot enable us to distinguish one object from another, a pure abstraction, and nothing more.
3. To solve the difficulties which attend the separation of the two ideas of extension and of body, it is necessary to determine the essence of body. When we can distinguish the essence of a body from its extension, the difficulty will be overcome, but not until then.
4. In order to understand the reason of this inseparability, it is necessary to remember what was said before, that extension is the basis of all other sensations; it is thesubstratumwhich is confounded with none, depends on none of them in particular, yet is an indispensable condition of them all.
I look at an apple, and examine the mutual relations of the sensations which it produces.
It is evident that though I abstract the smell, I do not thereby destroy any of the other sensations which it causes. Though it lose its odor, it is still extended, colored, it has a taste, and may produce a sound. I may also, in like manner, abstract its taste, its color, and all that relates to the sight, but I have still an object which is tangible, and consequently extended, figured, and possessed of all its other properties which affect the touch.
If instead of abstracting what relates to the sight, I abstract what belongs immediately to the touch, I may do this without destroying the other sensations; for I can still see the apple, its extension, form, and color.
I may even go farther, and strip the apple of all its sensible qualities, of its taste, smell, color, hardness, and whatever the senses can perceive, still there remains extension, not indeed sensible, but conceivable. Extension exists abstracted from its visibility, since it exists for the blind man: abstracted from its tangibility, since it exists for the sight; abstracted from odor, taste, and sound, since it exists for those who are deprived of these sensations, so long as they have sight or touch.
5. Here a difficulty arises. There seems to be a mistake in what we have said of the existence of extension abstracted from other sensations; for, although in making this abstraction we conceive ourselves to be deprived of these sensations, still we retain theimaginationof them; thus, when I strip the apple of all light and color, it is still extended; but that is because I still imagine a color, or, if I make a strong effort to destroy the color, it appears to me like a black object, on a ground of greater or less darkness, distinct from the apple. Does not this prove that there is an illusion in such abstractions, and that there is no complete abstraction, since the reality which we abstract is succeeded by the imagination of the same qualities, or of others which supply their place, so as to make the extension perceptible?
This objection is specious, and it would be difficult to give a satisfactory answer if the existence of men deprived of sight did not instantly dissipate it. No such imagination is possible in the case of a blind man, for him there is no color, no shade, no light, no darkness, nor anything which relates to sight, and still he conceives extension.
6. But at least, some one will answer, it must be confessed that the idea of extension is necessarily dependent on the sensations of touch; blind men also possess this sense, and by it they acquire the idea of extension. Therefore the idea of extension is inseparable from the sensations of touch. This argument is no better than the other; for, although we may acquire the idea of extension by the sense of touch, and this sense is all that is required to produce it, it is not true that this idea can only be acquired by touch. I have already proved that sight is sufficient of itself alone to produce the idea of the three dimensions which constitute a solid or extension in its full complement. But here I do not need the idea of a solid, that of a surface is sufficient; the extension of a surface is inseparable from sight. There is no sight without color, or light of some kind or other, and this cannot even be imagined without a surface.
I have another argument. Geometricians, doubtless, conceive extension, and yet they abstract all its relations to sight or touch; therefore, there is no necessary connection between them.
In any object submitted to the sight, what quality relating to the touch is necessary in order to produce the idea of extension? If we examine it closely, we shall find that there is none. Let us take a liquid; is its fluidity the necessary quality? No; for when congealed extension remains. Is it heat or cold? No; for without destroying its extension we may change its temperature as much as we please, no alteration is perceptible. Whatever quality relative to touch we may take, we shall find that it may be varied, modified, or entirely destroyed, without visibly affecting the extension.
It often happens that we have a clear and definite idea of the extension of an object without knowing any thing of its qualities in relation to touch. I see an object at a distance, I distinguish its color and its form, but I know not of what material it is, whether it is of marble, or wood, or wax, nor whether this material is hard or soft, moist ordry, warm or cold. I do not even know if it is tangible, as in the case of figures formed by vapors which are imperceptible to the touch.
7. Without extension there can be neither sight, nor touch, nor any other sensation. As to taste, it is clear that it requires touch, and cannot exist without it. Our assertion is less clear with regard to sound and smell; for, although we cannot separate these sensations from the idea of extension as they always involve this idea in one way or another, we do not know how it would be with a man who was deprived of all the other senses, and retained only those of smelling and hearing. But without speculating on this hypothesis, it is enough to know:
I. That nothing which is not extended can act upon our organs, unless by means wholly unknown to us, and which would give no idea of what we understand by body.
II. That even supposing the sensations of smelling and hearing to be possible without the idea of extension, they would in that case be only simple phenomena of our being, and would not place us in communication with the external world, as we now perceive it; because, if we should not know that they proceeded from another cause, we could have no more consciousness of them than that which we have of theme; and if we should know it, this cause would be represented to us only as an agent influencing us, and not by any means as a being having any thing similar to what we understand by body.
III. That in such a case we should have no idea of our own organization, nor of the universe; for it is clear that every thing being reduced to mere internal phenomena, and their relation to the agents producing them, and the idea of extension wanting, neither the universe nor our own body would be to us what they now are. What would the universe,—what would our body be without extension?
IV. That for the present we limit ourselves to the demonstration of the dependence which in the present system, of things, all sensations have in relation to extension; and this demonstration holds good, even though we suppose the man who possesses only the sense of smelling or that of hearing not to form any idea of extension, and not to need it in order to experience its sensations.
V. That even on this supposition, the proposition before established, that the idea of extension is independent of the other sensations, still remains unassailed.
VI. That the truth which we are principally endeavoring to demonstrate, that for us the idea of extension is inseparable from that of body, also stands firm.
8. This inseparability is so certain, that theologians explaining the august mystery of the Eucharist, distinguish in the extension of bodies the relations of the parts to each other, and their relation to place,in ordine ad se, et in ordine ad locum; and they say that the sacred body of our Lord Jesus Christ is in this august Sacrament, by extensionin ordine ad se, though not by extensionin ordine ad locum. This proves that the theologians saw that it is not possible for man to lose all idea of extension, without at the same time losing all idea of body; and thus they invented this ingenious distinction, of which I shall speak at greater length in another place.