Classical elements

The classificatory scheme develops in early natural philosophy: pre-Socratic thinkers propose single or multiple basic principles (e.g., Thales' water, Anaximenes' air, Heraclitus' fire). Empedocles posits four 'roots' (ῥιζώματα) as fundamental constituents. Plato adopts a technical vocabulary and Aristotle defines an element (στοιχεῖον, stoicheion) as a body into which other bodies may be analysed and which is not itself divisible into differently formed bodies. Later authors add aether (αἰθήρ) to account for celestial incorruptibility and motion.

As conceptual primitives the elements normally lack fixed anthropomorphic appearance. When depicted iconographically they use conventional signs—flame for fire, waves for water, soil or rocks for earth, clouds or wind for air, and ethereal light or bright vault for aether. Scholastic and alchemical diagrams arrange them geometrically (e.g., corners of a square) to show oppositions of sensible qualities.

The elements are not agents but explanatory principles: each is associated with two sensible qualities (classically: fire = hot + dry; air = hot + wet; water = cold + wet; earth = cold + dry) and these qualities explain tendencies such as burning, evaporation, solidity, and fluidity. Terrestrial elements interconvert and account for generation and corruption; aether is treated as incorruptible and subject to circular celestial motion. In medicine the elements map to the four humours (blood, yellow bile, black bile, phlegm), informing diagnostics and therapies aimed at restoring balance.