§32. (3) The body cannot originate such phenomena; and in fact the action of the rational soul is seen in its over-ruling the instincts of the bodily organs.
We add a further point to complete our demonstration for the benefit of those 148 who shamelessly take refuge in denial of reason. How is it, that whereas the body is mortal by nature, man reasons on the things of immortality, and often, where virtue demands it, courts death? Or how, since the body lasts but for a time, does man imagine of things eternal, so as to despise what lies before him, and desire what is beyond? The body could not have spontaneously such thoughts about itself, nor could it think upon what is external to itself. For it is mortal and lasts but for a time. And it follows that that which thinks what is opposed to the body and against its nature must be distinct in kind. What then can this be, save a rational and immortal soul? For it introduces the echo of higher things, not outside, but within the body, as the musician does in his lyre. 2. Or how again, the eye being naturally constituted to see and the ear to hear, do they turn from some objects and choose others? For who is it that turns away the eye from seeing? Or who shuts off the ear from hearing, its natural function? Or who often hinders the palate, to which it is natural to taste things, from its natural impulse? Or who withholds the hand from its natural activity of touching something, or turns aside the sense of smell from its normal exercise 149 ? Who is it that thus acts against the natural instincts of the body? Or how does the body, turned from its natural course, turn to the counsels of another and suffer itself to be guided at the beck of that other? Why, these things prove simply this, that the rational soul presides over the body. 3. For the body is not even constituted to drive itself, but it is carried at the will of another, just as a horse does not yoke himself, but is driven by his master. Hence laws for human beings to practise what is good and to abstain from evil-doing, while to the brutes evil remains unthought of and undiscerned, because they lie outside rationality and the process of understanding. I think then that the existence of a rational soul in man is proved by what we have said.
Compare the somewhat analogous argument in Butler, Serm. ii.