Apeiron

in the philosophy of Anaximander, a limitless, incommensurable, and boundless primary substance.

Anaximander’s concept was a step forward in developing the concept of matter compared to the theories prevailing at that time. These were propounded by Thales and Anaxi-menes, who held that the primary substance was one “element” (water or air). Anaximander’s concept was interpreted by Alexander of Aphrodisias as something between water and air or between fire and water or air. The Pythagoreans viewed it as the limitless, formless principle, which with its opposing “limit” constituted the basic grounds of being.