Take the concept of equality. We must admit that we have no experience, among sensible objects,
of exact equality; we see only approximate equality. How, then, do we arrive at the idea of
absolute equality? Or do we, perhaps, have no such idea?
Let us take a concrete case. The metre is defined as the length of a certain rod in Paris at a certain
temperature. What should we mean if we said, of some other rod, that its length was exactly one
metre? I don't think we should mean anything. We could say: The most accurare processes of
measurement known to science at the present day fail to show that our rod is either longer or
shorter than the standard metre in Paris. We might, if we were sufficiently rash, add a prophecy
that no subsequent refinements in the technique of measurement will alter this result. But this is
still an empirical statement, in the sense that empirical evidence may at any moment disprove it. I
do not think we really possess the idea of absolute equality that Plato supposes us to possess.
But even if we do, it is clear that no child possesses it until it reaches a certain age, and that the
idea is elicited by experience, although not directly derived from experience. Moreover, unless our
existence before birth was not one of sense-perception, it would have been as incapable of
generating the idea as this life is; and if our previous existence is supposed to have been partly
super-sensible, why not make the same supposition concerning our present existence? On all these
grounds, the argument fails.
The doctrine of reminiscence being considered established, Cebes says: "About half of what was
required has been proven; to wit, that our souls existed before we were born: --that the soul will
exist after death as well as before birth is the other half of which the proof is still wanting."
Socrates accordingly applies himself to this. He says that it follows from what was said about
everything being generated from its opposite, according to which death must generate life just as
much as life generates death. But he adds another argument, which had a longer history in
philosophy: that only what is complex can be dissolved, and that the soul, like the ideas, is simple
and not compounded of parts. What is simple, it is thought, cannot begin or end or change. Now
essences are unchanging: absolute beauty, for example, is always the same, whereas beautiful
things continually