“But,” it is urged,
“he does not know whether what he says is true.”
Neither do they, who assert that all things derive
their origin from fire or water or the four elements
or indivisible atoms; nor they who calculate the
distances of the stars or the size of the earth and sun.
And yet all these call the subject which they teach
an art. But if reason makes them seem not merely
to hold opinions but, thanks to the cogency of the
proofs adduced, to have actual knowledge, reason will
do the same service to the orator.