Jean Buridan - Questioner of Aristotle

Aristotle was the chief philosopher of Europe during the later half of the Middle Ages. But there were those who questioned him on various grounds. One of the areas in which he became dubious was in some of the details of physical law (what we would today call science).  One man who was part of that opposition was Jean Buridan. Buridan was not unique, but he was an example of one of various people who were calling into question Aristotle's opinions.

Buridan came from the position of William of Ockham, who held that categories of physical objects may have existence in the mind, but they are not something that exists in the physical world. He then proceeded to build up a philosophical system based on this. But along the way he questioned Aristotle's view on the flight of projectiles. Aristotle held that nothing moved unless there was something in contact pushing it. He therefore concluded that projectiles moved as a result of the air behind them pushing. Buridan claimed that a projectile was given an impetus when it was put in motion and continued to move until friction and gravity slowed it down enough to stop it. This was a major step toward the law of inertia, which in turn laid the foundation for the Copernican revolution.  The Aristotelian philosophy held that the planets moved in circles because they were made of ether, which naturally moves in that manner.  But ether was located in space because it sought to distance itself from the center of the earth, which in the Aristotelian view was the center of the universe. But if inertia was the correct way of understanding things, then objects in space could be moving because they started out moving and had not been slowed down yet. But if this was so, the center of the universe need not correspond to the center of the earth.

Perhaps even more fundamental was the change from abstract deduction to empirical observation as the way to understand the world. While this obviously fitted with Buridan's nominalism, which makes categories dubious, it also fits with Christianity, which claims the universe was created by God, who created it the way he wanted it to. This differs from the Greek idea that there is only one possible state of the universe, which could be deduced from basic principles. And while Buridan may have gone too far in the other direction in denying all categories, I am convinced that God had more freedom of choosing what to create than the Greeks allowed Him. Also, our current scientific knowledge would not lead us to see the physical world as a series of deductions from simple premises, but as a highly complex thing that boils down to a series of principles that blow our mind. And these things can only be investigated, not by abstract thinking, but going out and empirically investigating what they are.