according to Aristotle. Aristotle maintained that there are four elements—fire, air, water, and earth, and this assertion has been the subject of very unwise ridicule. Modern chemists maintain the same fact, but have selected four new words for the four old ones, and instead of the term “element,” use “material forms.” We say that matter exists under four forms: the imponderable (caloric), the gaseous (air), the liquid (water), and the solid (earth), and this is all the ancient philosophers meant by their four elements or elemental forms. It was Empedocles of Sicily who first maintained that fire, air, earth, and water are the four elements; but he called them Zeus, Hera, Goea, and Poseidon. (Latin, eleo for oleo. Vossius says: ab ant. eleo pro oleo, i.e. “cresco, quod omnia crescant ac nascantur.” Latin, elementum. to grow out of.)
Let us the great philosopher [Aristotle] attend. . . . His elements, `Earth, Water, Air, and Fire; . . . Tell why these simple elements are four; Why just so many; why not less or more?
The first of these forms—viz. “Caloric,” or the imponderable matter of heat, is now attributed to a mere condition of matter, like motion.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Elements from Infoplease: