Philosophical Dictionary, by Voltaire

SENSATION.

Oysters, it is said, have two senses; moles four; all other animals, like man, five. Some people contend for a sixth, but it is evident that the voluptuous sensation to which they allude is reducible to that of touch; and that five senses are our lot. It is impossible for us to imagine anything beyond them, or to desire out of their range.

It may be, that in other globes the inhabitants possess sensations of which we can form no idea. It is possible that the number of our senses augments from globe to globe, and that an existence with innumerable and perfect senses will be the final attainment of all being.

But with respect to ourselves and our five senses, what is the extent of our capacity? We constantly feel in spite of ourselves, and never because we will do so: it is impossible for us to avoid having the sensation which our nature ordains when any object excites it. The sensation is within us, but depends not upon ourselves. We receive it, but how do we receive it? It is evident that there is no connection between the stricken air, the words which I sing, and the impression which these words make upon my brain.

We are astonished at thought, but sensation is equally wonderful. A divine power is as manifest in the sensation of the meanest of insects as in the brain of Newton. In the meantime, if a thousand animals die before our eyes, we are not anxious to know what becomes of their faculty of sensation, although it is as much the work of the Supreme Being as our own. We regard them as the machines of nature, created to perish, and to give place to others.

For what purpose and in what manner may their sensations exist, when they exist no longer? What need has the author of all things to preserve qualities, when the substance is destroyed? It is as reasonable to assert that the power of the plant called “sensitive,” to withdraw its leaves towards its branches, exists when the plant is no more. You will ask, without doubt, in what manner the sensation of animals perishes with them, while the mind of man perishes not? I am too ignorant to solve this question. The eternal author of mind and of sensation alone knows how to give, and how to preserve them.

All antiquity maintains that our understanding contains nothing which has not been received by our senses. Descartes, on the contrary, asserts in his “Romances,” that we have metaphysical ideas before we are acquainted with the nipple of our nurse. A faculty of theology proscribed this dogma, not because it was erroneous, but because it was new. Finally, however, it was adopted, because it had been destroyed by Locke, an English philosopher, and an Englishman must necessarily be in the wrong. In fine, after having so often changed opinion, the ancient opinion which declares that the senses are the inlets to the understanding is finally proscribed. This is acting like deeply indebted governments, who sometimes issue certain notes which are to pass current, and at other times cry them down; but for a long time no one will accept the notes of the said faculty of theology.

All the faculties in the world will never prevent a philosopher from perceiving that we commence by sensation, and that our memory is nothing but a continued sensation. A man born without his five senses would be destitute of all idea, supposing it possible for him to live. Metaphysical notions are obtained only through the senses; for how is a circle or a triangle to be measured, if a circle or a triangle has neither been touched nor seen? How form an imperfect notion of infinity, without a notion of limits? And how take away limits, without having either beheld or felt them?

Sensation includes all our faculties, says a great philosopher. What ought to be concluded from all this? You who read and think, pray conclude.

The Greeks invented the faculty “Psyche” for sensation, and the faculty “Nous” for mind. We are, unhappily, ignorant of the nature of these two faculties: we possess them, but their origin is no more known to us than to the oyster, the sea-nettle, the polypus, worms, or plants. By some inconceivable mechanism, sensitiveness is diffused throughout my body, and thought in my head alone. If the head be cut off, there will remain a very small chance of its solving a problem in geometry. In the meantime, your pineal gland, your fleshly body, in which abides your soul, exists for a long time without alteration, while your separated head is so full of animal spirits that it frequently exhibits motion after its removal from the trunk. It seems as if at this moment it possessed the most lively ideas, resembling the head of Orpheus, which still uttered melodious song, and chanted Eurydice, when cast into the waters of the Hebrus.

If we think no longer, after losing our heads, whence does it happen that the heart beats, and appears to be sensitive after being torn out?

We feel, you say, because all our nerves have their origin in the brain; and in the meantime, if you are trepanned, and a portion of your brain be thrown into the fire, you feel nothing the less. Men who can state the reason of all this are very clever.

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Last updated Tuesday, March 4, 2014 at 18:25