archei

Archei, the plural form of archē in ancient Greek philosophy, denotes the fundamental principle or origin of all things. The term archē (archai being its Greek plural) comes from archē meaning “beginning” or “first principle” and was central to early cosmology and metaphysics. In pre-Socratic thought, thinkers proposed different archai as the ultimate substratum of reality: Thales held water as the archē, Anaximander proposed the apeiron (the indefinite or boundless), Anaximenes identified air as the archē, and Heraclitus argued that fire embodies the constant process of change.

Other thinkers, such as Parmenides and the Eleatics, argued for Being as the archē, while the Pythagoreans emphasized number as the archē of reality. The search for archeai reflects the ancient effort to explain change, continuity, and the nature of being beyond appearances.

In Aristotle's philosophy, archē is used to denote the primary source or principle of a thing's change or existence, including causes of movement and the source of being. The concept evolved into discussions of cosmology, natural philosophy, and metaphysics, influencing later philosophical and scientific thought.

Modern usage of archē/archai is largely historical; the related English term arche appears in discussions of presocratic philosophy. Note that Archaea, one of the three domains of life, is a separate term derived from the same Greek root but refers to a distinct biological group.