Then he heard some one reading out of a book of Anaxagoras, that mind is the cause of all things. And he said to himself: If mind is the cause of all things, surely mind must dispose them all for the best. The new teacher will show me this 'order of the best' in man and nature. How great had been his hopes and how great his disappointment! For he found that his new friend was anything but consistent in his use of mind as a cause, and that he soon introduced winds, waters, and other eccentric notions. (Compare Arist. Metaph.) It was as if a person had said that Socrates is sitting here because he is made up of bones and muscles, instead of telling the true reasonthat he is here because the Athenians have thought good to sentence him to death, and he has thought good to await his sentence. Had his bones and muscles been left by him to their own ideas of right, they would long ago have taken themselves off. But surely there is a great confusion of the cause and condition in all this. And this confusion also leads people into all sorts of erroneous theories about the position and motions of the earth. None of them know how much stronger than any Atlas is the power of the best. But this 'best' is still undiscovered; and in enquiring after the cause, we can only hope to attain the second best.
Now there is a danger in the contemplation of the nature of things, as there is a danger in looking at the sun during an eclipse, unless the precaution is taken of looking only at the image reflected in the water, or in a glass. (Compare Laws; Republic.) 'I was afraid,' says Socrates, 'that I might injure the eye of the soul. I thought that I had better return to the old and safe method of ideas. Though I do not mean to say that he who contemplates existence through the medium of ideas sees only through a glass darkly, any more than he who contemplates actual effects.'
If the existence of ideas is granted to him, Socrates is of opinion that he will then have no difficulty in proving the immortality of the soul. He will only ask for a further admission:that beauty is the cause of the beautiful, greatness the cause of the great, smallness of the small, and so on of other things. This is a safe and simple answer, which escapes the contradictions of greater and less (greater by reason of that which is smaller!), of addition and subtraction, and the other difficulties of relation. These subtleties he is for leaving to wiser heads than his own; he prefers to test ideas by the consistency of their consequences, and, if asked to give an account of them, goes back to some higher idea or hypothesis which appears to him to be the best, until at last he arrives at a restingplace. (Republic; Phil.)
The doctrine of ideas, which has long ago received the assent of the Socratic circle, is now affirmed by the Phliasian auditor to command the assent of any man of sense. The narrative is continued; Socrates is desirous of explaining how opposite ideas may appear to coexist but do not really coexist in the same thing or person. For example, Simmias may be said to have greatness and also smallness, because he is greater than Socrates and less than Phaedo. And yet Simmias is not really great and also small, but only when compared to Phaedo and Socrates. I use the illustration, says Socrates, because I want to show you not only that ideal opposites exclude one another, but also the opposites in us. I, for example, having the attribute of smallness remain small, and cannot become great: the smallness which is in me drives out greatness.
One of the company here remarked that this was inconsistent with the old assertion that opposites generated opposites. But that, replies Socrates, was affirmed, not of opposite ideas either in us or in nature, but of opposition in the concretenot of life and death, but of individuals living and dying. When this objection has been removed, Socrates proceeds: This doctrine of the mutual exclusion of opposites is not only true of the opposites themselves, but of things which are inseparable from them. For example, cold and heat are opposed; and fire, which is inseparable from heat, cannot coexist with cold, or snow, which is inseparable from cold, with heat. Again, the number three excludes the number four, because three is an odd number and four is an even number, and the odd is opposed to the even. Thus we are able to proceed a step beyond 'the safe and simple answer.' We may say, not only that the odd excludes the even, but that the number three, which participates in oddness, excludes the even. And in like manner, not only does life exclude death, but the soul, of which life is the inseparable attribute, also excludes death. And that of which life is the inseparable attribute is by the force of the terms imperishable. If the odd principle were imperishable, then the number three would not perish but remove, on the approach of the even principle. But the immortal is imperishable; and therefore the soul on the approach of death does not perish but removes.