Galileo Galilei (1564–1642) was an Italian natural philosopher, physicist, and astronomer. He defended the Copernican system in Dialogue Concerning the Two Chief World Systems, which included a series of arguments against Aristotelian astronomy. Most strikingly, he argued that the heavens and Earth had the same kind of motion and that it was not necessary to postulate a teleological—or goaldriven—system for celestial movement. That is, it was not necessary to claim, as Aristotle had done, that the movement of the heavenly bodies was caused by what they were striving for.