This is the the fifth post in my Theories of Knowledge and Reality series. Follow the link for more on the series and for links to other entries as they appear.
(Note: My presentation of these issues is somewhat influenced by Peter van Inwagen's chapter on idealism in his Metaphysics. I agree with his statement that the view Berkeley develops might better be thought of as ideaism, but he's also right that since there is a traditional label for the view, it's probably best to stick with it.)
George Berkeley gives what I consider to be the most creative response to Cartesian skepticism. He argues that we do know of the ordinary objects we believe exist, because those objects are just ideas in our minds. We certainly know of those ideas. I'll save the arguments for and against his view for the next post. In this post I just want to explain what the view amounts to.
Berkeley's idealism is something like thinking we're in the Matrix but without the computers that controlled everyone's experiences and without bodies out in the "real world". For Berkeley, all there is is the world of ideas. By 'ideas', he means the images we see, the sounds we hear, and so on. These objects of perception are items within our mind that we perceive directly. In the post after the next one, I'll compare Berkeley's view of perception with other theories of perception in his general time period, but for now just think of it as a development of Descartes. Descartes thought he could be sure that he existed, and he wanted to say also that he could be sure that certain things were going on in his mind. His Augustinian argument for his own existence also supports knowledge that he's thinking and knowledge about which things he's thinking. Augustine had said as much in his own discussions of skepticism.
What Descartes adds actually goes back to Epicurus, hundreds of years before Augustine. Epicurus talked about our perceptions as infallible. He didn't think we could ever be wrong about what we perceive. When you look more closely at what he's saying, it's not that radical, however, because he's not saying we can be sure that our perceptions are of the things they seem to be of. What we can be sure of is that the images in our minds look a certain way to us and that the sounds that strike our ears sound a certain way to us. He admits that the images might have been different before they got to our eyes (he thought of the image itself as traveling through the air and becoming modified in the process, which explains distortion over a distance or the appearance of bent oars in water due to what we now know as bent light).
The key idea here is that we're sure that we're seeing something a certain way, but once we add in the belief that it reflects the way things are out in the world we're going to be in the realm of belief. Epicurus explained that this is how we go wrong. If we have a belief that's false added to our perception, we will think we're perceiving wrongly. In reality, we're just adding a false belief to a perception that is indeed as we perceive it. Descartes pretty much could say everything he says in these terms, and then he'd be raising doubts about whether we have knowledge that our ideas are of what they seem to be of. His skeptical line of questioning in some places is almost exactly what the ancient skeptics said to the Epicureans. He just worries about how we would know which beliefs would then be ok to have. Epicurus said we just have a clear grasp of some, and those are sure, but scholars have a hard time trying to figure out what he meant by that and if he can really get away with it.
So Berkeley comes along and starts with the picture inherited from Descartes (through John Locke, who will take center stage in the aforementioned, upcoming theories of perception post). Once you have that picture, it's clear that all you really perceive directly is the world of ideas. But isn't that what happens in the Matrix? Neo sees things as if there's a world like what he sees, but there isn't one. Well, there is, Berkeley would say. It's in his mind though, and it's in the minds of everyone else in the Matrix. All the things they perceive are real. It's just that the only things they're perceiving are ideas. They aren't objects external to their minds. They're objects internal to minds, just shared among many minds.
Berkeley thinks this is what actually happens in the real world of everyday life. We have these perceptions of images in our minds, just as the people in the Matrix do, and this is basically what the world is like. All the ideas are coordinated, as they are in the Matrix, but by God and not by some artificial intelligence that wants to use human bodies for some scientifically implausible purpose. If you already believe that God created the universe in a way that there are things that we perceive through our senses, Berkeley just modifies the view slightly so that those objects are in our minds. They're real. Scientific understandings of the universe are worthwhile, because it tells us what the world is like. This is a world of ideas, but that's the world God created. The tables, trees, clouds, sun, roads, trains, elevators, pencils, and human bodies we interact with all the time are indeed real, and they're created by God just as people who believe in the external world believe. It's just that they're not independent of minds. They exist only in minds and derive their existence from the great mind who created the universe. People who believe God created already believe that anyway. They just add this external element to it, and Berkeley thinks that element is false.
What's even more interesting about Berkeley's view is that he insists that his view fits perfectly with the commonsense view of the world. We still talk about the sun rising when we know the earth goes around the sun and spins on its axis, creating just the appearance that the sun rises, but it's still true to say that the sun rises, because such statements are about what's going on in our perception. In the first-person experience of the sun rising, it really does rise. The fact that it isn't really rising but we're going around it doesn't change the truth of the statement, because the statement is about whatever it is that leads to our perception of it as rising.
This view is today called externalism about the content of language. What gives terms their meaning depends partly on the nature of the things they refer to, even if we don't know that nature. The word 'water' would refer to water even if we didn't know its chemical makeup and thought of it as a fundamental building block. Our concepts play some role in the meaning of terms, but what's really true plays enough of a role that we can say the sun is rising and be telling the literal truth because of what the expression really means.
Well, Berkeley says this will apply to everything we say about things we falsely believe to be external to us. The table my computer is sitting on is a table, and the computer is real. It's in front of me, in fact. Those statements are true. It's just that what they're referring to are objects in the world of ideas. The computer is an idea-object that the idea-objects called my fingers are currently typing on. What makes these things exist is that they're perceived, though they're not dependent on human perception, because God perceives all the ideas constantly and organizes them so that people's experiences are all coordinated with each other. Our language talks about all this, and in fact our statements are true unless we explicitly say that these things are external to us and not just to our bodies, which are in the world of ideas themselves, and within that world these things really are outside our bodies. So just about everything we ordinarily believe to be true is true, according to Berkeley. His view thus fits pretty well with common sense, he thinks, as strange as it initially sounds.
Why is this a response to skepticism, though? Isn't the skeptic questioning whether we know that external objects exist? Isn't Berkeley just giving in and denying that they exist? In one sense, yes. He's accepting that the thing Descartes isn't sure of isn't sure, because he's insisting that it's not even true. It is indeed a response to skepticism, however. Think about what Berkeley can be sure of. Descartes' skeptical arguments concede that you can be absolutely certain that you are having the experiences you're having. You know that you're perceiving things as if they're this way. Therefore, the things the skeptic says we know are exactly the things Berkeley says are all there is to know. If there's nothing further to know than what the skeptic says we can know, then we know all we wanted to know. Since the skeptic says we know we have ideas of trees in our perceptual field, and those trees are all there is to the trees themselves, then we can know that there are trees there. We see them. They're in our minds. We know all the things Descartes says we should doubt. This is indeed a response to skepticism. What remains to be seen is why we should believe it's correct.
In the next post, I'll look at two arguments for idealism and one argument against it.