Atomism (from Greek ἄτομον, atomon, i.e. "uncuttable, indivisible") is a natural philosophy proposing that the physical world is composed of fundamental indivisible components known as atoms. References to the concept of atomism and its atoms appeared in both ancient Greek and ancient Indian philosophical traditions. The ancient Greek atomists theorized that nature consists of two fundamental principles: atom and void. Clusters of different shapes, arrangements, and positions give rise to the various macroscopic substances in the world.