Overview

The theme of the second dialogue is how our sensations are caused. Hylas takes the position that they are caused by material external objects while Philonous will deny this makes sense.

I started with a handout that presents some important passages about ideas. First, there are passages from Descartes and Berkeley saying that the senses do not involve perceiving things but rather ideas in our minds. That is the cornerstone of Philonous’s constant refrain that he is the one who is defending common sense: you do, in fact, see sensible objects like trees and your senses cannot be wrong because what you are seeing is not a thing external to your mind but rather an idea inside your mind. By contrast, the materialists have trouble explaining how the thing you see, the idea, is related to the material thing outside the mind, the material tree.

I also included a passage in which Berkeley denies there are abstract ideas. He maintains that you cannot picture an extended object without all of its properties, like colors. That is, you cannot abstract extension apart from color, smell, and so on. This seems to me to be tied to an implicit assumption that ideas are mental images. Even then, I’m not sure it would be true. But it plays an important role in Berkeley’s argument.

Do objects exist when they are not perceived?

Philonous’s position raises an obvious question: do things exist when I am not perceiving them? His answer is that they do, but only because they are perceived by someone else, namely, God.

You would think that Philonous would include an explanation of how we have access to the ideas in God’s mind. That would fit the theme: how do what we call sensible objects cause the sensations that appear in our minds? But, alas, he does not.

Different attempts to explain how objects cause sensations

The bulk of the dialogue concerns Hylas’s attempts to explain how matter could be the cause of our sensory ideas.

For example, he considers something like Descartes’s argument that we use reason rather than the senses to discover the nature of bodies, like wax (519).

We get a version of occasionalism, a view that Malebranche (and Descartes) advanced (521).

And something like Locke’s view that matter is something unknown, without sensible qualities. (That would be Locke’s account of substance and real essences) (521-22).