"The skeptic will claim that if there is an external world, the things in it are observable because they exist, and not the other way around: that existence isn’t the same thing as observability. And although we get the idea of dreams and hallucinations from cases where we think we can observe the contrast between our experiences and reality, it certainly seems as if the same idea can be extended to cases where the reality is not observable. If that is right, it seems to follow that it is not meaningless to think that the world might consist of nothing but the inside of your mind, though neither you nor anyone else could find out that this was true. And if this is not meaningless, but is a possibility you must consider, there seems no way to prove that it is false, without arguing in a circle. So there may be no way out of the cage of your own mind. This is sometimes called the egocentric predicament. And yet, after all this has been said, I have to admit it is practically impossible to believe seriously that all the things in the world around you might not really exist. Our acceptance of the external world is instinctive and powerful: we cannot just get rid of it by philosophical arguments. Not only do we go on acting as if other people and things exist: we believe that they do, even after we’ve gone through the arguments which appear to show we have no grounds for this belief. (We may have grounds, within the overall system of our beliefs about the world, for more particular beliefs about the existence of particular things: like a mouse in the breadbox, for example. But that is different. It assumes the existence of the external world.)"