Classical essentialism

Classical essentialism was a theory of nature developed in ancient Greece, mainly by Aristotle (4th century BCE), to provide a metaphysical foundation for the science of that time. It sought to explain and synthesize Greek knowledge in fields as diverse as cosmology and biology. It was the cornerstone of Aristotle's metaphysics. Aristotle believed that the world below the sphere of the moon consists ultimately of four elements (earth, air, fire and water), while the heavens above are composed of a special element (the ether) that is essentially different from any of the others. Each natural kind of object, or substance, he thought, has its own special place in the cosmos, and its own natural motion. Thus, heavenly bodies were supposed naturally to move in circles (or combinations of circles) about the centre of the cosmos, while terrestrial bodies of the various kinds all had their proper places, and would naturally return to these places by the shortest paths should they be forced out of them. There were no forces required to maintain the circular motions of the stars or planets, Aristotle argued, and none were required to bring heavy objects back to earth, once they had been lifted up, for these motions were all natural motions. Forces would only be required to prevent them from occurring, or cause the bodies to move otherwise.