arkhê

Arkhe, or archē (Greek ἀρχή), is a philosophical term meaning beginning, origin, first principle, or source of rule. In ancient Greek thought it designated the fundamental principle from which all things arise or is governed. The word also appears in broader senses as the cause, explanation, or underlying substance of phenomena.

In Presocratic philosophy, archē was the central question: what is the archē of the cosmos? Different thinkers proposed diverse candidates. Thales argued that water is the archē of all things; Anaximenes claimed air; Anaximander suggested the apeiron, an indefinite or boundless principle; Heraclitus held fire as the ever-present archē underlying change. Some traditions, including early Pythagoreans, pointed to numbers or mathematical relations as the archē. Anaxagoras introduced nous (mind) as a governing principle that orders the cosmos.

In Aristotle, archê takes on a more systematic role as the first principle or source of being and change within a thing. There, archē is closely linked to the theory of causes: material, formal, efficient, and final. The archē explains why a thing exists in a particular way and how it comes to be, and it may refer to the underlying form or principle that organizes a substance. For Aristotle, archē thus functions as the rational basis for explanation and change in nature.

In later philosophy, archē continued to signify the ultimate principle or source, sometimes personified or framed as the supreme cause of reality. The term remains a key concept in discussions of substance, causation, and the origins of change, reflecting a long-standing inquiry into what underlies and unifies reality.