Errors concerning the movements of the fibres of our senses

Errors concerning the movements of the fibres of our senses.

The second thing found in each of the sensations is the vibration of the fibres of our nerves, which is communicated to the brain; and we deceive ourselves in that we always confuse this vibration with the soul’s sensation, and that we judge that there is no such vibration when we do not perceive it through the senses.

We do not perceive these movements, or that we confuse them with our sensations

We confuse, for example, the vibration that fire excites in the fibres of our hand with the sensation of heat, and we say that heat is in our hand: but because we do not feel the vibration that visible objects make upon the optic nerve at the back of the eye, we think that this nerve is not vibrated and that it is not covered with the colours we see; on the contrary, we judge that only the external object is covered with these colours. However, one can see by the following experiment that colours are almost as strong and as vivid on the back of the optic nerve as on visible objects:

III. Take the eye of a newly killed ox, remove the skins that are opposite the pupil at the place where the optic nerve is, and put in their place some piece of paper thin enough to be transparent; this done, place this eye in the hole of a window, so that the pupil is exposed to the air, and the back of the eye is inside the room, which must be well closed so that it is very dark; and then one will see all the colours of the objects outside the room spread over the back of the eye, but painted upside down. If it happens that these colours are not vivid enough, the eye must be lengthened by pressing it on the sides, if the objects painted on the back of the eye are too close, or else made shorter if the objects are too far away.

By this experiment one clearly sees that we should judge or feel colours at the back of our eyes, just as we judge that heat is in our hands, if our senses were given to us to discover the truth, and if we were guided by reason in the judgments we form about the objects of our senses.

But to give some reason for all the strangeness of our judgments about sensible qualities, we must consider that the soul is so closely united to its body, and has become so carnal since sin, that it attributes to it many things that belong only to itself, and it hardly distinguishes itself from it any more. So much so that it attributes to it not only all the sensations of which we now speak, but also the power of imagining, and even sometimes the power of reasoning; for there have been a great number of philosophers stupid and coarse enough to believe that the soul was only the finest and most subtle part of the body.

If one wishes to read Tertullian carefully, one will see only too many proofs of what I say, since he himself holds this opinion, following a great number of authors he cites. This is so true that he tries to prove in his book On the Soul that faith, Scripture, and even particular revelations oblige us to believe that the soul is corporeal; and we should not be surprised at this, since he fell into that excess of folly of imagining that God Himself was corporeal. I do not wish to refute these views, because I have assumed that one should have read some works of Saint Augustine or of Monsieur Descartes, which will have sufficiently shown the extravagance of these thoughts, and which will have sufficiently confirmed the mind in the distinction between extension and thought, between soul and body.

The soul is therefore so blind that it does not recognize itself, and does not see that its own sensations belong to it; but to explain this, we must distinguish in the soul three kinds of sensations: some strong and vivid, others weak and languid, and finally some midway between the others.

IV. The strong and vivid sensations are those that startle the mind and awaken it with some force, because they are very agreeable or very disagreeable to it; such are pain, tickling, great cold, great heat, and generally all those that are not only accompanied by traces in the brain, but also by some movement of the spirits toward the interior parts of the body, that is to say, by some movements of the spirits proper to excite the passions, as we shall explain elsewhere.

The weak and languid sensations are those that touch the soul very little, and are neither very agreeable nor very disagreeable to it, such as moderate light, all colours, ordinary and fairly faint sounds, etc.

Finally, I call midway between the strong and the weak those kinds of sensations that touch the soul moderately, such as a bright light, a violent sound, etc. Now, it must be noted that a weak and languid sensation can become moderate, and finally strong and vivid. The sensation of light, for example, is weak when the light of a torch is faint or the torch is far away; but this sensation can become moderate if one brings the torch close enough to us; and finally, it can become very strong and very vivid if one brings the torch so close to one’s eyes as to be dazzled by it, or when one looks at the sun. Thus the sensation of light can be strong, weak, or moderate, according to its different degrees.

V. Here then are the judgments that our soul makes about these three kinds of sensations, in which we can see that it almost always blindly follows the sensible impressions or the natural judgments of the senses, and that it delights, so to speak, in spreading itself over all the objects it considers, by stripping itself of what it has in order to clothe them with it.

The first of these sensations are so vivid and touching that the soul can hardly prevent itself from recognizing that they belong to it in some way, so that it not only judges that they are in the objects, but it also believes them to be in the limbs of its body, which it considers as a part of itself. Thus it judges that cold and heat are not only in the ice and in the fire, but that they are also in its own hands.

As for the languid sensations, they touch the soul so little that it does not believe that they belong to it, nor that they are within itself, nor in its own body, but only in the objects. It is for this reason that we take away light and colours from our soul and from our own eyes to adorn external objects with them, although reason teaches us that they are not found in the idea we have of matter, and experience shows us that we should judge them to be in our eyes as well as on objects, since we see them there as well as in objects, as I have proved by the experiment of an ox’s eye placed in the hole of a window.

Now, the reason why all men do not immediately see that colours, odours, flavours, and all other sensations are modifications of their soul is that we have no clear idea of our soul; for when we know a thing by the idea that represents it, we clearly know the modifications it can have. All men agree, for example, that roundness is a modification of extension, because all men know extension by a clear idea that represents it.

Thus, not knowing our soul by its idea, as I shall explain elsewhere, but only by the inner feeling we have of it, we do not know by simple vision, but only by reasoning, whether whiteness, light, colours, and other weak and languid sensations are or are not modifications of our soul. But as for vivid sensations, such as pain and pleasure, we easily judge that they are in us, because we feel well that they touch us, and we have no need to know them by their ideas in order to know that they belong to us.

As for the moderate sensations, the soul finds itself greatly embarrassed. For on one hand, it wishes to follow the natural judgments of the senses, and for that reason it distances from itself, as much as it can, these kinds of sensations in order to attribute them to objects; but on the other hand, it cannot help feeling within itself that they belong to it, especially when these sensations approach those I have called strong and vivid. So here is how it conducts itself in the judgment it makes about them: if the sensation touches it strongly enough, it judges it to be in its own body as well as in the object; if it touches it only very little, it judges it to be only in the object; and if this sensation is exactly midway between the strong and the weak, then the soul no longer knows what to believe, when it judges only by the senses.

For example, if one looks at a candle from a little distance, the soul judges that the light is only in the object; if one brings it very close to one’s eyes, the soul judges that it is not only in the candle but also in one’s eyes; but if one withdraws it to about a foot away, the soul remains for some time without judging whether this light is only in the object. But it never thinks, as it should, that light is not and cannot be a property or a modification of matter, and that it is only within itself; because it does not think to use its reason to discover the truth of what is the case, but only its senses, which never discover it and which are given only for the preservation of the body.

Now, the reason why the soul does not use its reason, that is to say, its pure intellection, when it considers an object that can be perceived by the senses, is that the soul is not touched by the things it perceives through pure intellection, whereas on the contrary it is very vividly touched by sensible things; for the soul applies itself strongly to what touches it much, and it neglects to apply itself to things that do not touch it. Thus, it almost always conforms its free judgments to the natural judgments of its senses.

To judge soundly, therefore, of light and colours, as well as of all other sensible qualities, one must carefully distinguish the feeling of colour from the movement of the optic nerve, and recognize, by reason, that movements and impulses are properties of bodies, and thus can be found in objects and in the organs of our senses; but that the light and colours we see are modifications of the soul, quite different from others, and of which we also have quite different ideas.

For it is certain that a peasant, for example, sees colours very well and distinguishes them from all things that are not colours; it is equally certain that he does not perceive any movement either in the coloured objects or at the back of his eyes. Therefore colour is not movement. Likewise, a peasant feels heat very well, and has a clear enough knowledge of it to distinguish it from all things that are not heat; yet he does not even think that the fibres of his hand are moved. The heat he feels is therefore not a movement, since the ideas of heat and movement are different, and he can have one without the other. For there is no other reason for saying that a square is not a circle than that the idea of a square is different from that of a circle, and that one can think of one without thinking of the other.

Only a little attention is needed to recognize that it is not necessary that the cause which makes us feel such or such a thing should contain it in itself. For just as there need not be light in my hand in order for one to see when I strike my eyes, neither is it necessary that there should be heat in the fire in order for me to feel it when I present my hands to it, nor that all the other sensible qualities I feel should be in the objects; it suffices that they cause some vibration in the fibres of my flesh, so that my soul, which is united to it, may be modified by some sensation. There is no relation between movements and feelings, it is true; but neither is there any between body and mind; and since nature, or the will of the Creator, unites these two substances, as opposed as they are by their nature, we should not be surprised if their modifications are reciprocal. It is necessary that this be so, in order that together they may form but one whole.

It must be carefully noted that since our senses are given to us only for the preservation of our body, it is very fitting that they should lead us to judge of sensible qualities as we do. It is much more advantageous for us to feel pain and heat as being in our body than if we judged that they were only in the objects that cause them, because pain and heat, being capable of harming our limbs, it is fitting that we should be warned when they are attacked by them, in order to prevent them from being injured.

But it is not the same with colours. They cannot ordinarily wound the back of the eye, where they are gathered, and it is useless for us to know that they are painted there. These colours are necessary to us only in order to distinguish objects more clearly, and it is for this reason that our senses lead us to attribute them only to objects. Thus, the judgments to which the impression of our senses leads us are very just, if considered in relation to the preservation of the body; but nevertheless, they are entirely strange and very far from the truth, as has already been seen in part and as will be seen even better in what follows.