The second is the method of reason, which was that of
the ancient philosophers, the pillars of wisdom; this is the
method of the understanding. They proved things by reason
and held firmly to logical proofs; all their arguments
are arguments of reason. Notwithstanding this, they differed
greatly, and their opinions were contradictory.
They even changed their views—that is to say, during
twenty years they would prove the existence of a thing by
logical arguments, and afterward they would deny it by
logical arguments—so much so that Plato at first logically
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proved the immobility of the earth and the movement of
the sun; later by logical arguments he proved that the sun
was the stationary center, and that the earth was moving.
Afterward the Ptolemaic theory was spread abroad, and
the idea of Plato was entirely forgotten, until at last a new
observer again called it to life. Thus all the mathematicians
disagreed, although they relied upon arguments of
reason. In the same way, by logical arguments, they
would prove a problem at a certain time, then afterward
by arguments of the same nature they would deny it. So
one of the philosophers would firmly uphold a theory for a
time with strong arguments and proofs to support it,
which afterward he would retract and contradict by
arguments of reason. Therefore, it is evident that the
method of reason is not perfect, for the differences of the
ancient philosophers, the want of stability and the variations
of their opinions, prove this. For if it were perfect, all
ought to be united in their ideas and agreed in their opinions.