Paradox of the Court

The Paradox of the Court, also known as the counterdilemma of Euathlus or Protagoras' paradox, is a paradox originating in ancient Greece. It is said that the famous sophist Protagoras took on a pupil, Euathlus, on the understanding that the student pay Protagoras for his instruction after he wins his first court case. After instruction, Euathlus decided to not enter the profession of law, and Protagoras decided to sue Euathlus for the amount owed.[1]

Protagoras argued that if he won the case, he would be paid his money. If Euathlus won the case, Protagoras would still be paid according to the original contract, because Euathlus would have won his first case. Euathlus, however, claimed that if he won, then by the court's decision he would not have to pay Protagoras. If, on the other hand, Protagoras won, then Euathlus would still not have won a case and would therefore not be obliged to pay. The question is then, which of the two men is in the right?

The story is related by the Latin author Aulus Gellius in Attic Nights.[2]