aer

In early Greek philosophy, Anaximenes of Miletus proposed that aer (air or vapor) was the fundamental substance of the universe. He believed that different forms of matter resulted from the condensation and rarefaction of air. When air is most evenly distributed, it is the invisible air we breathe. Through condensation, it becomes mist, water, and eventually solid matter like earth and stones. Conversely, rarefaction turns air into fire. Anaximenes also suggested that aer was divine and eternal, animating the universe much like the soul animates humans. His ideas represented a shift from mythological explanations to naturalistic ones, influencing later scientific thought by proposing that known natural processes could explain the world's origins. The term aer can also be a combining form meaning "air" or "gas".123