Book 4
1
From the same view proceeds the theory of Protagoras, and both alike must be either true or false. For if all opinions and appearances are true, everything must be at once true and false; for many people form judgements which are opposite to those of others, and imagine that those who do not think the same as themselves are wrong: hence the same thing must both be and not be.
2
And if this is so, all opinions must be true; for those who are wrong and those who are right think contrarily to each other. So if reality is of this nature, everyone will be right.
2
Clearly then both these theories proceed from the same mental outlook. But the method of approach is not the same for all cases; for some require persuasion and others compulsion.
3
The ignorance of those who have formed this judgement through perplexity is easily remedied, because we are dealing not with the theory but with their mental outlook; but those who hold the theory for its own sake can only be cured by refuting the theory as expressed in their own speech and words.
4
This view comes to those who are perplexed from their observation of sensible things. (1.) The belief that contradictions and contraries can be true at the same time comes to them from seeing the contraries generated from the same thing.
5
Then if what is not cannot be generated, the thing must have existed before as both contraries equally—just as Anaxagoras saysCf. Aristot. Met. 4.4.28. that everything is mixed in everything; and also Democritus, for he too saysCf. Aristot. Met. 1.4.9. that Void and Plenum are present equally in any part, and yet the latter is , and the former is not.
