History of Western Philosophy - Bertrand Russell [84]
The second argument is that knowledge is recollection, and therefore the soul must have existed before birth. The theory that knowledge is recollection is supported chiefly by the fact that we have ideas, such as exact equality, which cannot be derived from experience. We have experience of approximate equality, but absolute equality is never found among sensible objects, and yet we know what we mean by 'absolute equality'. Since we have not learnt this from experience, we must have brought the knowledge with us from a previous existence. A similar argument, he says, applies to all other ideas. Thus the existence of essences, and our capacity to apprehend them, proves the pre-existence of the soul with knowledge.
The contention that all knowledge is reminiscence is developed at greater length in the Meno (82 ff.). Here Socrates says, 'there is no teaching, but only recollection.' He professes to prove his point by having Meno call in a slaveboy whom Socrates proceeds to question on geometrical problems. The boy's answers are supposed to show that he really knows geometry, although he has hitherto been unaware of possessing this knowledge. The same conclusion is drawn in the Meno as in the Phaedo, that knowledge is brought by the soul from a previous existence.
As to this, one may observe, in the first place, that the argument is wholly inapplicable to empirical knowledge. The slave-boy could not have been led to 'remember' when the Pyramids were built, or whether the siege of Troy really occurred, unless he had happened to be present at these events. Only the sort of knowledge that is called a priori—especially logic and mathematics—can be possibly supposed to exist in every one independently of experience. In fact, this is the only sort of knowledge (apart from mystic insight) that Plato admits to be really knowledge. Let us see how the argument can be met in regard to mathematics.
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: That most accurate 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