a presocratic Greek philosopher and associate of Anaximander who believed that all things are made of air in different degrees of density (6th century BC)
a presocratic Greek philosopher and student of Thales who believed the universal substance to be infinity rather than something resembling ordinary objects (611-547 BC)
a presocratic Greek philosopher and astronomer (who predicted an eclipse in 585 BC) who was said by Aristotle to be the founder of physical science; he held that all things originated in water (624-546 BC)