Several sophists also questioned received wisdom about the gods and the Greek culture, which they believed was taken for granted by Greeks of their time, making them among the first agnostics. For example, they argued that cultural practices were a function of convention or nomos rather than blood or birth or phusis. They argued even further that morality 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.
