The George Berkeley Project
THE PROJECT: To avoid empirical skepticism by denying the existence of an external world of matter.
If you don't remember discussing Berkeley in class, you may have been gone that day. You may have not realized we were talking about Berkeley. You may not have been paying attention at all.
You may have sneezed and missed it.
In sort of a History of Philosophy coup d'etat, we demonstrated our commitment to not thinking much about Idealism by waving at Berkeley as we drove past in our Leibniz-powered Monadmobile. To be fair, however, Berkeley didn't do much for Idealism except assert its basic tenet, then get weird(er). For class, we read from Three Dialogues.
Pretending to be Plato, Berkeley constructs three dialogues between Hylas (matter) and Philonous (love of mind). Philonous presents Berkeley's position while Hylas represents common objections to the view.
Philonous' argument basically follows these lines: The only thing which the mind can perceive/attend to are its own ideas, NOT things in and of themselves. Thus, the mind deals only with its own ideas (perceptions) of the external world. It has an idea of objects, sensations, etc. All we have are these perceptions. Since these perceptions can obviously not exist without the mind, and since we only interact with our perceptions and not actual, material things, it follows that our only world is the world inside our heads, and various "objects" are just what we call groups of stable perceptions.
Berkeley seems to think he has a problem in that, if a person ceases to pay attention to a particular perception (for example, you go outside so you are no longer perceiving the inside of your room), that perception ceases to exist. Where does it go, and how does it come back into existence again when you turn your mind toward it? Like Descartes, who created this whole subject/object problem in the first place, Berkeley needs God to bail him out.
God is always perceiving all possible perceptions. Thus, when you have an idea of leaving your room, God is still having the idea of being inside your room, so it's still existing for you when you return (i.e. perceive it again).
Keep in mind that Berkeley is not denying the existence of anything else besides him. He's denying the existence of matter. The world as we know it exists; it is just a world of mental images and perceptions -- it cannot exist without the mind.