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. § 6. That we may not go crooked as he has done, and that we may form the soundest conception possible of the soul of all animals, without excepting man, who is of the same nature, and who only exercises different functions from the difference in his organization, it is important to attend to the following remarks. It is certain that there exists in the universe a very subtle fluid, a substance extremely attenuated, whose source is the sun, and which pervades all other bodies, less or more, according to their nature and their consistence. Such is the soul of the world, which governs and vivifies it, and of which some portion is distributed to all the creatures in the universe. [60] This soul is the purest fire. It burns not of itself, but by different movements, which it communicates to the particles of other bodies into which it enters, it burns and makest its warmth be felt. Our visible fire contains more of this matter than air; air, more than water; and earth, considerably less than any of them. Plants have more of it than minerals, and animals more than either. In fine, this fire pervading the body renders it capable of thought, and is that properly termed the soul, although it sometimes receives the appellation of animal spirits, which permeate the whole body. It is certain therefore that this soul being of the same nature as that of animals, is annihilated at the death of man, as it is at that of the other creatures. It follows that whatever poets and divines have told us of a future state, is only the chimerical offspring of their own brain, begotten and nourished by them for purposes which is by no means difficult to fathom. CHAPTER VI ON THE SPIRITS CALLED DEMONS § 1. We have explained in another place how the notion of spirits came to be introduced among men, and proved that they were merely phantoms which existed only in their disordered imagination.