Empiricism can never tell what is true or false

In Plato's theory of knowledge, Socrates debates the view that man is the measure of all things and that we know by way of sensation. There are several reasons he gives for why these ideas are false. One, however, reason why it is false to say that man is the measure of all things is that it cuts itself off the branch. If whatever a man thinks is true and no one thinks false ideas then guess what? All ideas are true. So whether I think one thing is true or you say another is true both are true no matter if we disagree or think differently. This is the problem with knowledge by sensation. It can never give us any reason to think one man is wrong over another or another man is right or true in opinion over another. This is the point Gordon Clark draws out against sense perception as a way of knowing between good and evil. At best sensation might help me to know the way things are at the moment but can never tell me how it ought to be.