 Theophrastus says that Diogenes was the last of the physical philosophers, the physiologoi, or “inquirers into nature,” as Aristotle called them; Diogenes Laertius (Lives II.16–17) gives that title to Archelaus, saying that he was the teacher of Socrates (see Betegh 2013a). There was also another group of thinkers active about this time: the Sophists. Many of our views about this group have been shaped by Plato’s aggressively negative assessment of them: in his dialogues Plato expressly contrasts the genuine philosopher, i.e., Socrates, with the Sophists, especially in their role as teachers of young men growing into their maturity (youths at the age when Socrates, too, engaged with them in his discussions). Modern scholarship (Woodruff and Gagarin 2008, Kerferd 1981, Guthrie 1969) has shown the diversity of their views. They were not completely uninterested in the theoretical problems that concerned others of the Presocratics. Gorgias of Leontini questioned the possibility of the certainty that Parmenides sought. In his On Nature, or On what-is-not, Gorgias claims that nothing satisfies (or can satisfy) Parmenides’ requirements for what-is (Mansfeld 1985, Mourelatos 1987b, Palmer 1999, Caston 2002, Curd 2006). Protagoras, too, doubted the possibility of the strong theoretical knowledge that the Presocratics championed. The Sophists raised ethical and political questions: Does law or convention ground what is right, or is it a matter of nature? They traveled widely, sometimes serving as diplomats, and they were both entertainers and teachers. They gave public displays of rhetoric (this contrasts with Diogenes of Apollonia’s comments about his book, which seems to imply a more private  enterprise)[12]  and took on students, teaching both the art of rhetoric and the skills necessary for succeeding in Greek political life. With the Sophists, as with Socrates, interest in ethics and political thought becomes a more prominent aspect of Greek philosophy.