Leucippus (first half of 5th century BC) was an Ionian Greek who belonged to the same Ionian School of naturalistic philosophy as Thales, Anaximander, Anaximenes, and he was interested in reality and not idealism. Around 440 or 430 BC he founded a school at Abdera. He was one of the earliest Greeks to develop the theory of atomism, the idea that everything is composed entirely of various imperishable, indivisible elements called atoms. According to this atomism, if you take a piece of wood and then cut it in to two equal parts, then do it continuously, eventually you will find a part that you can't cut. This smallest possible part is the "atom". Leucippus is a shadowy figure, as his dates are not recorded and he is often mentioned in conjunction with his more well-known pupil Democritus, who replaced indeterminism with determinism as the ontological cause of atomic movement. It is therefore difficult to determine which contributions come from Democritus and which come from Leucippus.