Metrodorus of Chios (4th century BC) was a Greek Presocratic philosopher, belonging to the school of Democritus, and an important forerunner of Epicurus.
Metrodorus was a pupil of Nessus of Chios, or, as some accounts prefer, of Democritus himself. He is said to have taught Diogenes of Smyrna, who, in turn, taught Anaxarchus.
Metrodorus was a complete sceptic. He accepted the Democritean theory of atoms and void and the plurality of worlds, but held a theory of his own that the stars are formed from day to day by the moisture in the air under the heat of the Sun. According to Cicero he said, "We know nothing, no, not even whether we know or not" and maintained that everything is to each person only what it appears to him to be. Metrodorus is especially interesting a forerunner of Anaxarchus, and as a connecting link between atomism proper and the later scepticism.
The following quote is attributed to him. If accurate, it demonstrates that Metrodorus had a cosmological philosophy that was advanced for the ancient world: "A single ear of corn in a large field is as strange as a single world in infinite space."