Page "Law of noncontradiction" Paragraph 19

This way, he accomplishes two essential goals for his philosophy.

First, he logically separates the Platonic world of constant change from the formally knowable world of fixed physical objects.

Second, he provides the conditions for the dialectic method to be used in finding definitions, as for example in the Sophist.

So Plato's law of noncontradiction is the empirically derived necessary starting point for all else he has to say.