In the Phaedo, Plato gives us a picture of Socrates’ last day.  He is on death row, waiting for his execution.  His friends and followers have assembled to console and support him through his trial.  Plato provides an extended philosophical discussion focusing on the question of immortality of soul.  Is the soul immortal?  Is there an afterlife?  Simmias and Cebes are the skeptics, worried that the soul is mortal and perishable.  Socrates bravely takes up the argument against their objections.  His objectors provide a series of ever more devastating arguments to the contrary.  Socrates, unfazed, meets each one calmly and rationally, and provides strong reasons for believing that the soul is everlasting, and not dependent on the body for its existence. 

            Socrates’ arguments are not just a continuation of the kinds of arguments found in Plato’s Socratic dialogues.  Plato appeals to the Theory of Recollection, introduced in the Meno as inspired by a religious doctrine.  The soul, according to this theory, is reincarnated into different bodies.  It retains tacit knowledge from previous lives.  When we seem to arrive at knowledge from ourselves, that is a manifestation of our recollecting truths from previous lives.  For instance, when we observe things with our senses, we notice that some objects are equal to each other in size.  But we are also aware that no two physical objects are perfectly equal.  So we seem to have an awareness of a perfect equality which we never experience directly.  We must, then, have a knowledge of Equality itself that is somehow prior to our sense experience.  There must, accordingly, be certain ideals that we are acquainted with in some way other than by sense perception. 

            We all encounter these ideal Forms.  We know them by a kind of knowledge that is independent of sense experience.  And we seem to carry this knowledge with us in our migration from body to body.  We now have the elements of three interlocking theories: the Theory of Forms, which attributes a kind of ideal existence to certain principles; the Theory of Recollection, according to which we retain a knowledge of the Forms; and the Theory of Immortality, and specifically a theory of Reincarnation, according to which the soul inhabits different bodies and retains some sort of knowledge from its wanderings.  The first is a theory of reality, a metaphysical theory; the second a theory of knowledge, an epistemological theory, the third a theory of soul and mind, a psychological theory. 

            Although Plato puts these theories in the mouth of Socrates, none of them is a Socratic theory.  Socrates, as far as we can see from Plato’s early dialogues and other early sources, is a philosopher who occupies himself solely with moral theories.  He believes that we have souls, but he does not speculate on the nature of the soul, or even the question of immortality.  He seems to believe that there is knowledge, but he does not subscribe to any particular theory of knowledge.  He believes that there are virtues and virtuous people, but he does not subscribe to any particular metaphysical theory to account for what virtues are.  Plato himself seems to have been deeply impressed by Socrates’ moral theory and his belief in the pursuit of moral improvement.  But Plato seems to think that, without some body of truths about reality, knowledge, and mind, we cannot arrive at a reliable moral theory. 

            In the Meno, Plato has Socrates borrow theories of immortality, reincarnation, and recollection from certain religious sages.  In the Symposium, he has Socrates claim he borrowed from a wise woman of Mantinea a theory of Forms and a conception of Beauty.  Here in the Phaedo, Plato puts these speculations in the mouth of Socrates, and makes them, by implication, his own.  He emerges from Socrates’ shadow as the architect of a new vision of reality. 

            Plato’s vision starts from a commitment to ideal entities, the Forms, that are designed to supply the basis for the properties a thing has, and a value theory which will leave no room for relativism or personal prejudices.  The Forms are eternal, objective realities with some sort of hierarchical structure such that the Good stands at the pinnacle of existence and value.  Souls are everlasting, in touch with the ultimate realities, sometimes more directly, often indirectly, but capable of attaining to a secure knowledge of them which will provide a conceptual map of the world and a moral compass for life. 

            We glimpse the basis of a cosmology, reviving the project of the Presocratics to discover how the natural world arose and how it functions.  This project Socrates had abandoned as too remote from the pressing concerns of moral improvement.  But now that Plato has established moral principles as guideposts of action and souls as receptacles of morality, Plato sees the possibility of a cosmos that aims at the Good as a goal.  Plato will not take up the challenge to rewrite cosmology until late in his career, in the dialogue Timaeus, but when he does, he will provide a model for later philosophers of how to construct a cosmos that embodies what is best in the world.  The Socratic movement with its turn to morality and humanity—its moral humanism—will not renounce cosmology, but will ultimately embrace it in a humanized, moralized natural science.