MICROCOSM and MACROCOSM. — The term microcosm, from the Greek μικρός “small” and κόσμος “world,” was first used by Democritus (H. Diels, *Vorsokratiker*, Berlin 1922, 55 B 34) and later especially by the Stoics (Plutarch, *De stoicorum repugnantibus*, 44), as a definition of man, inasmuch as within him there is a synthesis of the natural elements and an image of the whole.
By inverse analogy, already by the early Ionian philosophers (Anaximenes, Heraclitus, Empedocles) and then by Plato with extensive allegory (*Tim.*, 30–38), the world had been conceived as a great animated organism, thus giving rise, albeit less distinctly, also to the opposite term mega- or macro-cosm (μέγας, μακρός “great”). For Aristotle (*De An.*, III, 8, 431 b 21) and later for Scholasticism (*Sum. Theol.*, 1a, q. 84, a. 2, ad 2), the soul is in some way the universe, inasmuch as through sensitive and intellectual knowledge it can assimilate all things. Through Boethius (*De diffinitione*: PL 64, 907) the term entered Christian literature, which regards man (*parvus mundus*) not only as an image of the sensible universe but in some way of the whole creation, including the angels and even the deity itself. The Renaissance, with its parallel reevaluation of nature and man, revived the idea in a naturalistic sense, and the concept of man as the mirror and quintessence of the universe appears frequently in Nicholas of Cusa (*De docta ignor.*, III, 31), Cardano, Campanella (*De sensu rer.*, I, 10), G. Bruno, and others.
In the modern age, although the concept was not abandoned, its formulation lost importance, while the term microcosm was at times applied to the atom described by Bohr as a small planetary system.