The classical Greek quaternity: fire, air, water, earth.
Earth, Water, Air, and Fire — the four elements arranged by Empedocles and systematised by Aristotle through pairs of qualities: hot and cold, wet and dry. Each element is a particular combination, and transformation means shifting qualities.
This scheme unlocks combinatorial classification: a small grid of properties generating every substance, and a logic for why things change into one another. For two thousand years it organised medicine, temperament, and matter itself. Its lasting gift is the idea that complexity can be reduced to a few axes of difference — that the world is a table of combinations.