Leucippus (; Λεύκιππος, Leúkippos; fl. 5th century BCE) was a pre-Socratic Greek philosopher. He is traditionally credited as the founder of atomism, which he developed with his student Democritus. Leucippus divided the world into two entities: atoms, indivisible particles that make up all things, and the void, the nothingness that exists between the atoms. He developed his philosophy as a response to the Eleatics, who believed that all things are one and the void does not exist. Leucippus's ideas were influential in ancient and Renaissance philosophy. Leucippus was the first Western philosopher to develop the concept of atoms, but his ideas only bear a superficial resemblance to modern atomic theory. Leucippus's atoms come in infinitely many forms and exist in constant motion, creating a deterministic world in which everything is caused by the collisions of atoms. Leucippus described the beginning of the cosmos as a vortex of atoms that formed the Earth, the Sun, the stars, and other celestial bodies. As Leucippus considered both atoms and the void to be infinite, he presumed that other worlds must exist as cosmoses are formed elsewhere. Leucippus and Democritus described the soul as an arrangement of spherical atoms, which are cycled through the body through respiration and create thought and sensory input. The only records of Leucippus come from Aristotle and Theophrastus, ancient philosophers who lived after him, and little is known of his life. Most scholars agree that Leucippus existed, but some have questioned this, instead attributing his ideas purely to Democritus. Contemporary philosophers rarely distinguish their respective ideas. Two works are attributed to Leucippus (The Great World System and On Mind), but all of his writing has been lost with the exception of one sentence.
Life Almost nothing is known about the life of Leucippus. He was born in the first half of the 5th century BCE, and he presumably developed the philosophy of atomism during the 430s BCE, but the exact dates are unknown. Though he was a contemporary of the philosopher Socrates, Leucippus is categorized as a pre-Socratic philosopher because he continued the pre-Socratic tradition of physical inquiry that began with the Milesian philosophers. Leucippus is traditionally understood to have been a student of Zeno of Elea, though various ancient records have suggested Melissus of Samos, Parmenides, and Pythagoras as possible instructors of Leucippus. No students of Leucippus have been confirmed other than Democritus. Epicurus has been described as a student of Leucippus, but Epicurus has also been said to have denied the existence of Leucippus. Abdera, Elea, and Miletus have all been suggested as places where Leucippus lived, but these are most likely described as his home city because of their associations with other philosophers: Miletus was associated with the Ionian School that influenced Leucippus, Elea was associated with the Eleatic philosophers whom Leucippus challenged, and Abdera was the home of his student Democritus. Some 20th-century classicists such as Walther Kranz and John Burnet have suggested that he lived in all three cities—that he was born in Miletus before studying under Zeno in Elea and then settling in Abdera.
Philosophy
Atoms Leucippus is credited with developing the philosophical school of atomism. He proposed that all things are made up of microscopic, indivisible particles that interact and combine to produce all the things of the world. The atoms postulated by Leucippus come in infinitely many shapes and sizes, although the size and shape of each atom is fixed and unchanging. They are in a state of constant motion and continuously change arrangements with one another. He reasoned that there must be infinite types of atoms because there is no reason why there should not be. According to the 4th-century BCE philosopher Aristotle, Leucippus argued that logically there must be indivisible points in everything. His reasoning was that if an object was made entirely of divisible points, then it would not have any structure and it would be intangible. Leucippus developed atomism along with his student, Democritus; while Leucippus is credited with the philosophy's creation, Democritus is understood to have elaborated upon it and applied it to natural phenomena. Two works are attributed to Leucippus: The Great World System and On Mind. The former may have originally been titled The World System and then later renamed to avoid confusion with Democritus's The Little World System. Leucippus's The Great World System has sometimes been attributed to Democritus. Only one extant fragment is attributed to Leucippus, taken from On Mind: "Nothing happens at random, but everything for a reason and by necessity". Leucippus believed that all things must happen deterministically, as the positions and motions of the atoms guarantee that they will collide in a certain way, invoking the principle of causality. This was reminiscent of the 6th-century BCE philosopher Anaximander's argument that movement is created by differences, and it was later codified by the 17th-century philosopher Gottfried Wilhelm Leibniz with the principle of sufficient reason. Leucippus rejected the idea that there was an intelligent force governing the universe.
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