Anaximenes (585 BC - 525 BC)

Claiming that the unifying element within nature is the air, or aer (a mist-like gas for which aether makes the purer version), Anaximenes is the first to offer a theory by which the original source and support of everything which is changes into a multifarious reality. Due to his mechanistic view on how the governing processes of rarefaction and condensation bring about change and ensure the functioning of the universe, Anaximenes is sometimes regarded as a proto-atomist. The Greek material monist is the first one to put forth a theory of the soul and to also employ the microcosm/macrocosm argument in his natural philosophy: "Just as our soul, being air, holds us together, so do breath and air encompass the whole world."