Now Cebes helps Socrates out by “reminding” him of a theory he sometimes appeals to. “According to this theory, we have learned in an earlier age things that we now recollect. This would be impossible unless we had a soul that existed before we were born in human form.”[4] Simmias asks what the evidence is, and Cebes points out that you can show someone a geometrical diagram and extract knowledge from the person. This aside seems designed to remind the reader of the slave boy example in the Meno, where Socrates helps an uneducated slave boy to “remember” truths that allow him to solve a geometrical problem.[5]
Socrates takes over and points out that, for instance, in having an experience of equal things like sticks and stones, we recognize that they are not perfectly equal, or equal in all respects to all observers.[6] In effect, we also acknowledge the existence of Equality Itself, distinct from the things that have, or almost have, equal measurements. If you can judge sensible objects to fall short of a standard of equality, then you must have prior knowledge of that that standard. “Before we began to see and hear and have other perceptions,” Socrates concludes, “we must have acquired knowledge that the Equal Itself exists, so that we could compare equal objects from perception to the standard, because they were all striving to attain to it, while falling short.”[7]
We acquired our senses as soon as we were born. But we already had an awareness of standards like Equality. So we must have had knowledge of these standards before we were born. Now either we were born with the knowledge of Forms fully active, or we “forgot” this knowledge and had to recover it by recollection. But people are not fully aware of them, or they would not need to be “taught” geometry and the like. But we have already established that we had knowledge of the Forms before we were born. So our souls must exist prior to our birth into mortal bodies.
We must suppose that the Forms, such as Equality, always exist, and that we are aware of them in some way prior to our birth. If the Forms do not exist, then the present argument would be vain. But Simmias finds the argument wholly persuasive for the existence of Forms.
In this argument we glimpse the close theoretical connection between Plato’s account of reality, the Theory of Forms, and his account of knowledge, the Theory of Recollection. We also see his psychology entering in, with the Theory of Immortality. The soul is immortal, and able to grasp the eternal Forms; it enters into a human body, but outlives it. He has not at this point addressed the issue of Reincarnation, with the possibility of the soul entering into a series of bodies and outliving them. But he clearly is committed to a soul that pre-exists and outlives the body it inhabits.
We have here, apparently for the first time, an account of what would come to be known as a priori knowledge, according to which some knowledge, at least, comes to us independently of sense experience, and indeed in some sense makes sense experience possible. We may, it is true, learn something like arithmetic by learning to count and to play with numbers. We find two stones plus two stones make four stones; two sticks plus two sticks make four sticks, and from this we may discover that 2 + 2 = 4. But there is a sense in which the truths of arithmetic and certain other sciences are independent of our learning process. It is different, for instance, from our learning that all swans are white (which, we now know, happens to be a false statement).
At this point, however, Simmias objects that Socrates has proved only half of his case. He has shown, that the soul exists before the body it inhabits, and that it exists in the body. But he has not shown that it survives the body. It might, for all Socrates has said, perish when its body perishes.
Here Socrates says that we can establish the immortality of the soul if we combine the Recollection Argument with the Argument from Opposites. Since opposites come from opposites, and death comes from life, life must come from death. But the Argument from Opposites is less persuasive. Though it never gets mentioned, that argument fails to establish that the life that succeeds death is the same life that preceded it: is the soul identical through all its putative transformations?
[4] Plato Phaedo 72e-73a.
[5] Plato Meno 82b-86c; see above, ch. 14.2*.
[6] It is not clear whether Plato is talking of physical differences in objects or mental differences in perception; for our purposes, either interpretation will do.
[7] Plato Phaedo 75b.