In c.545BC, Anaximenes theorized that the “arche” or source and cause of everything, out of which out of which all things are made, was aer, variously translated as “mist, vapor or air”; air, according to Anaximenes, when rarefied, became fire, and when condensed became water and earth, as follows:

He theorized this, supposedly, per reasoning that because animals need air to breath, that this must be the original source of life. [1] This can be compared to Anaximander, who theorized that what he called the “apeiron”, which differentiated into water, earth, and fire, was the arche, and Thales, who said that water was the arche. Anaximenes model has since been truncated to an air is the first principle of everything philosophy.