Anaximenes

Anaximenes was an ancient Greek philosopher from the 6th century BCE, part of the Milesian school along with Thales and Anaximander. He believed that the fundamental substance underlying all things was air, which could change in density and form to create different elements and objects. For example, when compressed, air becomes water or earth, and when expanded, it becomes fire. His view suggests that everything in the universe arises from a single, invisible, and limitless source—air—through processes of rarefaction and condensation, emphasizing a natural, unifying principle behind the diversity of the world.