or immorality of any action could not be judged outside of the cultural context within which it occurred. The well-known phrase, "Man is the measure of all things" arises from this belief. One of their most famous, and infamous, doctrines has to do with probability and counter arguments. They taught that every argument could be countered with an opposing argument, that an argument's effectiveness derived from how "likely" it appeared to the audience (its probability of seeming true), and that any probability argument could be countered with an inverted probability argument. Thus, if it seemed likely that a strong, poor man were guilty of robbing a rich, weak man, the strong poor man could argue, on the contrary, that this very likelihood (that he would be a suspect) makes it unlikely that he committed the crime, since he would most likely be apprehended for the crime. They also taught and were known for their ability to make the weaker (or worse) argument the stronger (or better). Aristophanes famously parodies the clever inversions that sophists were known for in his play The Clouds. The word "sophistry" developed strong negative connotations in ancient Greece that continue today, but in ancient Greece sophists were nevertheless popular and well-paid professionals, widely respected for their abilities but also widely criticized for their excesses. Isocrates Isocrates (436–338 BC), like the sophists, taught public speaking as a means of human improvement, but he worked to distinguish himself from the Sophists, whom he saw as claiming far more than they could deliver. He suggested that while an art of virtue or excellence did exist, it was only one piece, and the least, in a process of self-improvement that relied much more heavily on native talent and desire, constant practice, and the imitation of good models. Isocrates believed that practice in speaking publicly about noble themes and important questions would function to improve the character of both speaker and audience while also offering the best service to a city. In fact, Isocrates was an outspoken champion of rhetoric as a mode of civic engagement. He thus wrote his speeches as "models" for his students to imitate in the same way that poets might imitate Homer or Hesiod, seeking to inspire in them a desire to attain fame through civic leadership. His was the first permanent school in Athens and it is likely that Plato's Academy and Aristotle's Lyceum were