Eubulides of Miletus (Greek: Εὑβουλίδης; fl. 4th century BCE) was a philosopher of the Megarian school, and a pupil of Euclid of Megara. He is famous for his paradoxes.
He was a contemporary of Aristotle, against whom he wrote with great bitterness. He taught logic to Demosthenes, and he is also said to have taught Apollonius Cronus, the teacher of Diodorus Cronus, and the historian Euphantus.
The Liar (pseudomenos) paradox
A man says: “What I am saying now is a lie.” If the statement is true, then he is lying, even though the statement is true. If the statement is a lie, then he is not actually lying, even though the statement is a lie. Thus, if the speaker is lying, he tells the truth, and vice versa.