Apeiron

Apeiron (ἄπειρον) is the term that the pre-Socratic philosopher Anaximander of Miletus used, around the 6th century BC, to designate the origin or first principle (arché) of all things. Its etymology means «unlimited», «indefinite» or «indeterminate», formed from the negative prefix a- and peiras, «limit». It was one of the great innovations of early Greek philosophy: the first principle was no longer a concrete element such as Thales' water, but a formless, indeterminate and boundless reality, which is neither water, nor earth, nor fire, nor air.

The apeiron is eternal, immortal and indestructible; it does not age or decay, and from it new materials constantly arise, from which everything we perceive is formed. From its depths the opposites—hot and cold, wet and dry—separate, and their struggle gives rise to the cosmos. According to the surviving fragments, the world is born, develops and perishes within the apeiron according to a necessity that Anaximander expressed in terms of justice (dike) and retribution: whatever prevails over its opposite must later pay the «penalty» of returning to the indefinite. Anaximander is also said to have held that infinite worlds are generated and destroyed within the same domain.

The notion draws on the Greek mythical tradition, such as the primordial Chaos of Hesiod's cosmogony, which is likewise an undetermined void, and on Near Eastern accounts of a formless, watery original world. Yet its formulation marks a move toward abstract, rational thought, in which natural forces are explained without appealing directly to divine figures, although the language remains partly mythical.

Anaximander's work has been almost entirely lost, and the apeiron is known through fragments and later commentaries, such as those of Simplicius, Aetius and Hippolytus, which has given rise to divergent interpretations. The Pythagoreans reworked the concept by associating it with the mathematical unit, and in later philosophy it has inspired very different readings, from Nietzsche's pessimistic interpretation to Heidegger's. In the twentieth century, Max Born proposed calling «apeiron» the primordial substance behind the elementary particles that Werner Heisenberg described as different quantum states of a single reality, an analogy that shows the lasting force of Anaximander's intuition.