I. Wherein is the Criterion for the Apprehension of the Soul.
All things that exist are either known by sense [442] or apprehended by thought. [443] And what falls under sense has its adequate demonstration in sense itself; for at once, with the application, it creates in us the impression [444] of what underlies it. But what is apprehended by thought is known not by itself, but by its operations. [445] The soul, consequently, being unknown by itself, shall be known property by its effects.