I. Wherein is the Criterion for the Apprehension of the Soul.

All things that exist are either known by sense ¹ or apprehended by thought. ² And what falls under sense has its adequate demonstration in sense itself; for at once, with the application, it creates in us the impression ³ of what underlies it. But what is apprehended by thought is known not by itself, but by its operations. ⁴ The soul, consequently, being unknown by itself, shall be known property by its effects.