Protagoras of Abdera he was a Greek sophist, an expert in rhetoric who toured the Greek world charging high fees for his knowledge of the correct use of words. Plato called it a "professional sophist" (the use of words to succeed).
Such was his success that he even created a School of sophists in which he profited handsomely from his teachings. We don't know the reason but he admitted to Enatlus , a young man without resources, under his tutelage to instruct him in the art of words. Since Enatlus could not pay him, they signed an agreement whereby the young man would pay for his classes when he had won the first case.
Enatlus was a brilliant student and finished teaching him without any problem, but seeing that the world of commerce was more lucrative, he left the law aside with the logical anger of the teacher. He continually reminded him of the debt contracted and the student replied:
After I win my first cause, master!
Protagoras got tired of waiting and took him to court. Before starting the process, Protágoras took the floor:
Judges! Either I win or I lose this case!
If I win, you must pay me because the sentence is in my favor; if I lose, you must still pay me, because you have won your first cause, as established in our agreement.
Enatlus was lost… but he proved that he had been a good disciple. He took the floor and, using the teacher's arguments, said:
Judges! Either I lose or I win this case!
If I lose, I don't have to pay anything because I lost my first case, according to the established agreement; And if I win, I won't have to pay anything either because the sentence is in my favor.
This «war of sophists » left the judges baffled and unable to pass sentence.
Source:Fun and Curious Mathematics – Malba Tahan Image:FiloPsico