The ancient city of Athens didn’t have a police force. Thus, if somebody committed a crime against you – if, for example, they embezzled your money or stole your property – the only way you could achieve justice was by taking them to court.
Ancient Athens also didn’t have any lawyers. Thus, anyone who found himself in court had to be prepared to argue the case himself.
One thing that ancient Athens did possess was plenty of unscrupulous characters. Many of these less-than principled folk discovered that if you were clever enough you could persuade the court to agree with you even if you were in the wrong (especially if your opponent was not very bright).
In the latter half of the fifth century BC, a group of teachers arose in Athens called Sophists. The Sophists claimed to be able to teach students how to prove impossible propositions, such as that nothing exists or that motion is impossible.