Primarily a teacher of rhetoric, Gorgias is generally classed as a Sophist. He came to Athens in 427 bc as an ambassador from his home town in Sicily, and his distinctive antithetical style had considerable literary influence. Philosophically he had serious interests in the science of the day, and wrote a treatise On That Which is Not, or Nature which is known only through summaries. It contained an extension of the Eleatic arguments against motion and in favour of unity, to prove the impossibility of nature existing at all; it is a matter of scholarly debate whether he believed this result (if, indeed, it is possible to believe it), or whether the treatise was a rhetorical exercise. His Encomium of Helen is the first clear treatment of the problem of free will.