The philosophers and scientists of the ancient world and the Middle Ages believed that the world we inhabit was entirely made up of four elements: earth, air, fire, and water. Aristotle added a fifth element, the aether or ether, by which he meant the material that fills the rest of space, mostly invisibly but sometimes taking the form of stars and planets. Many writers described the element as a kind of invisible light or fire. In the Middle Ages, it was referred to as the quinta essentia ("fifth element"). It isn't surprising that the quinta essentia came to stand for anything so perfect that it seemed to surpass the limitations of earth. Today we generally use quintessential rather freely to describe just about anything that represents the best of its kind.