Eubulides of Miletus (Ancient Greek: Εὐβουλίδης; fl. 4th century BCE) was a Greek philosopher of the Megarian school, a pupil of Euclid of Megara and a contemporary of Aristotle. He is famous for his logical paradoxes.
Eubulides was a pupil of Euclid of Megara, the founder of the Megarian school. 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. He may have been the author of a book about Diogenes of Sinope.
Eubulides is most famous for inventing the forms of seven famous paradoxes, some of which, however, are also ascribed to Diodorus Cronus:
The first paradox (the Liar) is probably the most famous, and is similar to the famous paradox of Epimenides the Cretan. The second, third and fourth paradoxes are variants of a single paradox and relate to the problem of what it means to "know" something and the identity of objects involved in an affirmation (compare the masked-man fallacy). The fifth and sixth paradoxes are also a single paradox and is usually thought to relate to the vagueness of language. The final paradox attacks presumptions involved in a proposition, and is related to the syllogistic fallacy.
These paradoxes were very well known in ancient times, some are alluded to by Eubulides' contemporary Aristotle and even partially by Plato. Aulus Gellius mentions how the discussion of such paradoxes was considered (for him) after-dinner entertainment at the Saturnalia, but Seneca, on the other hand, considered them a waste of time: "Not to know them does no harm, and mastering them does no good."