Overview

I introduced modern philosophy by characterizing some features of ancient thought that were challenged by the philosophers in this historical period. In particular, we looked at some of Galileo’s remarks about what he took to be the fundamental elements of the world.

Moderns vs. ancients

Here are three Aristotelian doctrines that were all challenged during the modern period (Rutherford 2006, 16–18).

1. The distinction between celestial objects and those on Earth. Celestial objects are eternal and unchanging; if they move, it is in perfect circles around the Earth. Things on earth, by contrast, are subject to generation and decay or corruption.

2. Things are composites of form and matter. Matter is stuff with no specific characteristics; it is “pure potentiality.” When it is united, matter forms substances. So-called forms give matter shape, properties, and the ability to act. A thing’s nature is its ability to cause things to happen and move. And a substance’s form determines the goal of its natural motions: rocks naturally fall down, fire naturally goes up, plants naturally reproduce themselves, and so on.

3. Human beings are distinguished from other animals because they are rational. There is an ethical component to rationality, since that involves the ability to choose between good and bad.

The modern period in philosophy involves questions about all three.

Galileo

The theme of the course is materialism and its problems. Galileo provides a nice starting point.

He draws a distinction between things that exist apart from our perception of them, such things that occupy space, and things that exist only because we perceive them, such as heat (Galilei [1623] 2019, 22).

His argument is that when your hand touches someone else’s body, the other person feels things like tickles. But the tickles are not qualities of your hand. They are produced by the person who is being touched (Galilei [1623] 2019, 22). He claims that the same thing cannot be said about shape and other physical dimensions.

The underlying view is that what is real is stuff that you can measure and express in numerical terms. That is, things that have qualities like size, shape, and motion (Galilei [1623] 2019, 23).

Philosophy is written in this grand book, the universe, which stands continually open to our gaze. But the book cannot be understood unless one first learns to comprehend the language and read the letters in which it is composed. It is written in the language of mathematics, and its characters are triangles, circles, and other geometric figures without which it is humanly impossible to understand a single word of it; without these, one wanders about in a dark labyrinth.¹

Of course, we do perceive things like colors, smells, tastes, and feelings. How do we do that if they aren’t real? And why are they correlated with the real things: the bodies? Galileo offers an explanation in terms of corpuscles, “little bodies” in Latin.