Apeiron (ἄπειρον) — “The unlimited,” “the indefinite,” or “the boundless”; a Greek term formed from the privative prefix a- and peras (“limit,” “boundary”). It names the principle (arché) proposed by Anaximander of Miletus (~610–546 BCE), a pupil of Thales, as the substrate and origin of all things. Unlike Thales (who posited water) or Anaximenes (air), Anaximander argued that no determinate element can be the principle of everything: if the ground were, say, water, it could not generate its own opposite, fire. The principle must therefore itself be indeterminate in quality, unlimited in extent, eternal, and in perpetual motion. Out of this indefinite ground the opposites (hot/cold, dry/moist) separate off, and their tension and balance constitute the natural world. In the sole surviving fragment of Anaximander—preserved by Simplicius and regarded as the oldest text of Western philosophy—it is said that things, as they perish, return to that from which they were born “according to necessity; for they pay penalty and retribution to one another for their injustice according to the assessment of time.” The cosmology sketched here replaces mythical explanation with an impersonal law governing coming-to-be and passing-away. The apeiron inaugurates the search for a single principle of physis that defines the Milesian school, and it prepares later concepts such as arché and, eventually, the problem of being and becoming.
← Glossary