Engraving of The Four Elements from a series entitled: Mythological Subjects by Jacob Matham, 1588. Many philosophies and world views have a set of classical elements believed to reflect the simplest essential parts and principles of which anything consists or upon which the constitution and fundamental powers of anything are based. Most frequently, classical elements refer to ancient beliefs inspired by natural observation of the phases of matter; with the classical elements: earth is equivalent to solid, water is equivalent to liquid, air is equivalent to gas and fire is equivalent to plasma. Prior to Empodocles, Greek philosophers had debated which substance was the primordial element from which everything else was made; Heraclitus championed fire, Thales supported water, and Anaximenes plumped for air. Anaximander argued that the primordial substance was not any of the known substances, but could be transformed into them, and they into each other. Empedocles was the first to propose four elements, fire, earth, air, and water. He called them the four roots.