Thesis 1: Reason is, as Brandom would say, an inferential activity.
This means: Reason connects general ideas with concrete experiences.
Thesis 2: But if reason connects, it is an activity that attempts to relate speakers to each other. In terms, of Socrates it attempts to relate their souls. Though hidden behind their walls of an impenetrable body – their city– rationality is the connection and the divide between the cities of souls.
Truth cannot be gained by reason alone.