Final answer:
Aristotle believed that the heavens were composed of the four elements: earth, air, fire, and water, because he thought that nature tended toward perfection and that the heavens would be made up of the purest elements.
Step-by-step explanation:
Aristotle believed that the heavens were composed of the four elements: earth, air, fire, and water. He thought that these elements made up the celestial bodies and the celestial sphere. Aristotle believed this because he thought that the heavens were made up of the same substances as the Earth, and that nature tended toward perfection, so the heavens would be composed of the purest elements.