The Phaedo, at least superficially, has to do with the immortality of the human soul. In order to prove that the soul is immortal, Plato has Socrates “prove” both that the soul exists before birth and that it exists after death. In order to prove that the soul exists before birth, Socrates relies on his theory of anamnesis, or recollection. For instance, regarding equality and the notion of deficiency, Socrates says “we must have had some previous knowledge of equality before the time when we first realized, on seeing equal things, that they were striving after equality, but fell short of it” (75a). Implicit in an acceptance of this theory is the assumption that such things as True Equality actually exist. In other words, it is implied that the theory of Forms is in fact true. While many readers may question either claim at the outset, Plato (as Socrates) offers no particular proof of it, so there really isn’t much we can usefully do to refute it. There follows a very particular “proof,” using these claims as premises, that the soul must have existed before birth. In this proof, Plato commits a logical fallacy that makes the remainder of his argument contingent on a single, baseless assumption.

The proof begins with the assertion that we could not have had any notion of deficiency before we began using our senses, “so it must be as a result of the senses that we obtained the notion that all sensible equals are striving to realize actual equality but falling short of it.” While this assertion may not be true, it at least seems more likely than that we somehow acquired a notion of deficiency before ever using our senses. Plato/Socrates goes on to say, “So before we began to…perceive equals, we must…have acquired the knowledge of equality as it really is; otherwise we could never have realized…that all equal objects of sense are desirous of being like it, but are only imperfect copies” (75b). That is, he claims that because we could not have had a notion of deficiency until after we began using our senses, we must have had a notion of equality before we began using our senses.

The problem with this claim is that, from the fact that we must have been able to perceive deficiency only after using our senses, it does not follow that we have been able to perceive deficiency from the first moment we used our senses. There is no reason to assume that, because a notion of deficiency depends on sensory perception, sensory perception must necessarily involve a notion of deficiency. It is quite plausible, in fact, that there was some length of time after birth, during which our senses functioned properly and yet we had no notions of anything at all. (It is hard to imagine a newborn baby seeing that two sticks of the same length are trying to achieve equality but are not truly equal.) If there was such a period of time, then it is entirely possible that we acquired the knowledge of equality some time between birth and the development of a notion of deficiency. Newborns magically learning the nature of equality may seem unlikely, but it is no less likely than newborns perceiving deficiency from the moment they begin perceiving anything.

However, there is no reason given here that should lead us to reject Plato’s claim as being false. The claim is just not necessarily true, but rather contingent on the truth of the assumption that we have had a notion of deficiency as long as we’ve used our senses. The soul’s existence before birth may necessarily follow from this assumption, but because the assumption is nowhere proven, we do not necessarily have any knowledge of equality at the moment of birth, and so the soul does not necessarily exist before birth. If the soul does not acquire knowledge of the Form of Equality before birth, then there is no reason to believe that this (or any other) form exists eternally wherever the soul might go after death, and it is possible that the soul can never perceive the forms directly (assuming they exist in the first place). If the soul cannot have direct knowledge of the forms, then nearly all of Plato’s theories of metaphysics, philosophy, and education become entirely meaningless.