But the path of early reasoners is beset by thorny entanglements, and he will not proceed a step without first clearing the ground.

This leads him into a tiresome digression, which is intended to explain the nature of contradiction.

First, the contradiction must be at the same time and in the same relation.

Secondly, no extraneous word must be introduced into either of the terms in which the contradictory proposition is expressed: for example, thirst is of drink, not of warm drink.

He implies, what he does not say, that if, by the advice of reason, or by the impulse of anger, a man is restrained from drinking, this proves that thirst, or desire under which thirst is included, is distinct from anger and reason.