Socrates was a classical Greek philosopher who is credited to have laid the fundamentals of modern western philosophy. He was interested in morality, and interpersonal relations. He believed that truth and absolute standard existed, and that reason could discover them.
However, he opposed the Sophists who were public speakers, gifted with speech, and skilled in rhetoric. They did not pursue the truth, but pursued to persuade. It didn’t matter if what they said was right or wrong, they only cared about winning public speeches, debates, and lawsuits. They said there was no moral absolute, so you could act in your best interest. They charged fees to those who wanted to learn to persuade and speak like them. Their doctrine was the Protagoras’ doctrine that said, “Man is the measure of all things”. This meant that man was the one who was able to say if something was right or wrong even if it wasn’t.
Socrates said that if Protagoras’ doctrine is true, then he cannot say those who disagree with him are wrong, because their disagreement is true for them.
Socrates asked questions and sought definitions; he searched for the truth, for what justice truly was. That is why he disagreed with the Sophists; he couldn’t believe that the truth was what you thought it was, but that there was really a one true truth.