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 subsequently especially by the Stoics (Plutarch, De stoicorum repugnantiis, 44), as a definition of man, insofar as in him there is a synthesis of the natural elements and an image of the whole.
By an inverse analogy, from the earliest Ionian philosophers (Anaximenes, Heraclitus, Empedocles) and subsequently in Plato, with an extensive allegory (Tim., 30–38), the world had been conceived as a great living organism, thus giving rise, although less distinctly, also to the opposing term mega- or macrocosm (μέγας, μακρός “great”). For Aristotle (De An., III, 8, 431 b 21) and subsequently for Scholasticism (Sum. Theol., 1°, q. 84, a. 2, ad 2), the soul is in some way the universe, insofar as through sensory and intellectual knowledge it can assimilate all things to itself. Through Boethius (De diffinitione: PL 64, 907), the term entered Christian literature, which considers man (parvus mundus) not only as an image of the sensible universe, but in some way of all creation, including the angels, and of the divinity itself. The Renaissance, with its parallel reassessment of nature and man, takes up the idea in a naturalistic sense, and the concept of man as the mirror and quintessence of the universe frequently appears in Cusanus (De docta ignor., III, 31), Cardano, Campanella (De sensu ver., I, 10), G. Bruno, etc.
In the modern age, although the concept was not abandoned, its formulation lost importance, while the term microcosm came at times to be applied to the atom described by Bohr as a small planetary system.