If our souls survive us, how, you ask, has the air contained them from eternity? How, I answer, does the earth contain so many bodies buried during so long a time? Just as corpses, after remaining for a while in the earth, change, and are dissipated to make room for others; so also the souls, liberated into air, remain for a little, and then are changed, diffused, rekindled, and resumed into the universal productive spirit; and so give way to others who come to take their places. This may serve for an answer, on the supposition that the soul survives the body. But we have not merely to consider the number of bodies thus buried in the earth. There are also all the living creatures eaten day by day by ourselves and other animals. How great a multitude of them is thus consumed, and as it were buried in the bodies of those who feed upon them. Yet there is ever space to contain them, owing to the changes into blood, air, and fire. What, then, is the key to this enquiry? Discrimination of matter and cause.