The philosopher with his head in the clouds — literally. Anaximenes (fl. mid-6th century BCE) declared air the primal stuff of everything. Stretch it, condense it, shake it around — voilà: matter. He took his teacher Anaximander’s abstract apeiron and gave it a breeze of familiarity. Sky turns to stone? Air pressure. Fire to water? Density. A true early materialist with a poetic streak, Anaximenes gave nature a breath of fresh thought.