A sophist was a professional travelling teacher in ancient Greece in the fifth and fourth centuries BC. Sophists specialized in one or more subject areas, such as philosophy, rhetoric, music, athletics, mathematics, and arete: "virtue" or "excellence". The sophists sold their tutoring expertise predominantly to young statesmen and nobility. Certain sophists are regarded as philosophers in their own right. The first credited sophist, Protagoras, argued that "man is the measure of all things", and he controversially would strive to "make the weaker argument the stronger".