The superiority which men arrogate over other animals, is chiefly founded upon their opinion, that they have the exclusive possession of an immortal soul. But ask them what this soul is, and they are puzzled. They will say, it is an unknown substance—a secret power distinct from their bodies—a spirit, of which they have no idea. Ask them how this spirit, which they suppose to be like their God wholly void of extension, could combine itself with their material bodies, and they will tell you, they know nothing about it; that it is to them a mystery; that this combination is an effect of the omnipotence of God. These are the ideas that men form of the hidden, or rather imaginary substance, which they consider as the main spring of all their actions!

If the soul is a substance essentially different from the body, and can have no relation to it, their union would be, not a mystery, but an impossibility. Besides, this soul being of a nature different from the body, must necessarily act in a different manner; yet we see that this pretended soul is sensible of the motions experienced by the body, and that these two substances, essentially different, always acts in concert. You will say that this harmony is also a mystery. But I will tell you, that I see not my soul, that I know and am sensible of my body only, that it is this body which feels, thinks, judges, suffers, and enjoys; and that all these faculties are necessary results of its own mechanism, or organization.