"By comparing them."
"With what?"
"With the thoughts of great men."
"And does he perceive truth in agreement with others, or in opposition to them?"
"In agreement with them."
"And where do those live with whom he is in agreement?"
"All around him."
"Have not others lived before him?"
"Certainly."
"And can we compare our thoughts and views with those men who have lived before us, or learn directly from the past?"