Why do the flames shoot lightly upward, while the earth presses downward with its weight, if it is not that these motions and situations are suitable to their respective natures? Moreover, each several thing is preserved by that which is agreeable to its nature, even as it is destroyed by things inimical. Things solid like stones resist disintegration by the close adhesion of their parts. Things fluid like air and water yield easily to what divides them, but swiftly flow back and mingle with those parts from which they have been severed, while fire, again, refuses to be cut at all. And we are not now treating of the voluntary motions of an intelligent soul, but of the drift of nature. Even so is it that we digest our food without thinking about it, and draw our breath unconsciously in sleep; nay, even in living creatures the love of life cometh not of conscious will, but from the principles of nature. For oftentimes in the stress of circumstances will chooses the death which nature shrinks from; and contrarily, in spite of natural appetite, will restrains that work of reproduction by which alone the persistence of perishable creatures is maintained. So entirely does this love of self come from drift of nature, not from animal impulse.