2.1 Recap of General Philosophy Lecture 1

What this lecture covers

This short lecture recaps the previous two and a half lectures before moving on to new material. It restates why the 17th and 18th centuries are pivotal for philosophy and why the problems from that period remain relevant today.

Millican summarizes how the medieval worldview, dominated by Aristotle and the Bible, explained physical behavior on the model of desire or striving, and how this broke down under pressure from Galileo's telescopic observations and from the emptiness of 'striving' as an explanation. He then recaps Descartes's mechanical alternative, in which matter's essence is extension and all motion takes the form of vortices, used to explain why the Moon and planets orbit rather than travel in straight lines.

Key ideas

• Aristotle's two-tier physics: earthly bodies strive toward the center of the universe, while heavenly bodies made of ether strive to move in circles.
• Empty explanations: appealing to desires or strivings explains nothing, since it can be used to justify any observed behavior after the fact.
• Galileo's telescope: observations of lunar craters, Jupiter's moons, and the phases of Venus contradicted the Aristotelian theory of a perfect, unchanging heaven.
• Mechanism: the 17th-century replacement theory, in which physical things act through contact, pressure and impact rather than desire.
• The orbit problem: inertia implies bodies move in straight lines unless a force acts on them, leaving orbital motion unexplained.
• Descartes's vortices: because matter is pure extension, empty space is impossible, so all motion takes the form of circulating vortices that carry planets and moons around.

Before you watch

• This lecture assumes you have watched lectures 1.2, 1.3 and 1.4, which it summarizes.

Check your understanding

1. Why is 'things strive to do X' considered an empty explanation?
2. What did Galileo's telescope reveal that contradicted Aristotelian astronomy?
3. How does Descartes use the idea that matter is extension to explain planetary orbits?