Brief Thoughts on the Phaedrus
Why does Socrates spend so much effort defining and describing the soul in so much detail in the Phaedrus? He tells us outright, in the dialogue. It is because no man can gain true knowledge from a speech, if the orator does not himself know how his speech is going to guide the soul to its first memory of the unified reality of beauty, found in the divine realm. Dialectic is the way to wisdom, and dialectic can only be achieved through speech. So, a speech needs to be crafted and delivered in such a way that it both provokes and then satisfies the desire to know beauty (or truth, or goodness).
