§ 5.
Diogenes believed that the soul was composed of air, whence he deduces the necessity of respiration. He defines it as an air which passes through the mouth into the pulmonary vessels, whence it becomes warm, and whence it is distributed to every part of the system.
Leucippus and Democritus assert that it is fire, and that, like fire, it is composed of atoms which readily penetrate all parts of the body, and communicate motion to it.
Hippocrates said that it was composed of water and of fire. Empedocles thought that it was compounded of the four elements. Epicurus believed with Democritus that the soul is composed of fire, but he adds that there enter into its composition, air, a vapour, and an indescribable substance, which is the principle of thought. Out of these four different substances he makes to himself a very subtle spirit, pervading all the body, and which, he says, we ought to term the soul.
Descartes reasons also, but in a very wretched manner, that the soul is not material. I say in a very wretched manner, for never did philosopher reason so badly on this subject as did this great man. Here is his argument. He sets outs by saying that he must doubt in the existence of his own body, believing that there exists no such thing as a body at all, and then he reasons in this fashion: “There exists no body; I exist nevertheless: I am therefore not a body, and consequently I can only be a substance which thinks.” Although this fine reasoning destroys itself sufficiently, I will yet take the liberty of giving my opinion of it in two words.
1. The doubt which M. Descartes assumes is indefensible; for although one may sometimes think that he does not think that he has a body, it is true nevertheless that he has a body, since he thinks of it.
2. Whoever believes that there exists no body, ought to be well assured that he is not one himself; for no one can doubt in his own existence. If he is assured in this matter, his doubt is useless.
3. When he says that the soul is a substance which thinks, he tells us nothing new. Every person agrees in this; but the difficulty is to ascertain the nature of that substance which thinks, and in this respect M. Descartes is no wiser than his predecessors.