‘Conflicts with philosophers’ outlines some of the disagreements Galileo had with natural philosophers. In 1604 Galileo had a feud with a philosopher over the distance of a supernova from the Earth. In 1609 Galileo learnt of a new invention that magnified the heavens. He created his own version, and used it to discover that the moon had mountains and craters. This enthralled the public, but enraged other philosophers, who would not accept that the moon was anything less than perfectly spherical. He also observed phases of Venus, which destroyed the Aristotelian and Ptolemaic arrangements of planets. Unlike philosophers, Galileo treated mathematics as a tool in the study of physics.