Brandeis University, Philosophy Department
Fall 2003
Brandeis University Web Stite

Philosophy 1A

Introduction to Philosophy

Professor Andreas Teuber
Prof. Teuber

What's To Know?

Thomas Nagel
What Does It All Mean? A Very Short Introductron to Philosophy
Oxford University Press, London and New York, 1987center>

Ordinarily you have no doubts about the existence of the floor under your feet, or the tree outside the window, or your own teeth. In fact most of the time you don't even think about the mental states that make you aware of those things: you seem to be aware of them directly. But how do you know they really exist? Would things seem any different to you if in fact all these things existed only in your mind-if everything you took to be the real world outside was just a giant dream or hallucination, from which you will never wake up? . . .

How can you know that isn't what's going on? If all your experience were a dream with nothing outside, then any evidence you tried to use to prove to yourself that there was an outside world would just be part of the dream. If you knocked on the table or pinched yourself, you would hear the

knock and feel the pinch, but that would be just one more thing going on inside your mind like everything else. It's no use: If you want to find out whether what's inside your mind is any guide to what's outside your mind, you can't depend on how things seem-from inside your mind-to give you the answer.

But what else is there to depend on? All your evidence about anything has to come through your mind-whether in the form of perception, the tes timony of books and other people, or memory- and it is entirely consistent with everything you're aware of that nothing at all exists except the inside of your mind....

Some would argue that radical skepticism of the kind I have been talking about is meaningless, be' cause the idea of an extemal reality that no one could ever discover is meaningless. The argument is that a dream, for instance, has to be something from which you can wake up to discover that you have been asleep; a hallucination has to be something which others (or you later) can see is not really there. Impressions and appearances that do not correspond to reality must be contrasted with others that do correspond to reality, or else the contrast between appearance and reality is meaningless.

According to this view, the idea of a dream from which you can never wake up is not the idea of a dream at all: it is the idea of reality-the real world in which you live. Our idea of the things that exist is just our idea of what we can observe. (This view is sometimes called verificationism.) Sometimes our observations are mistaken, but that means they can be corrected by other observations-as when you wake up from a dream or dis cover that what you thought was a snake was just a shadow on the grass. But without some possibility of a correct view of how things are (either yours or someone else's), the thought that your impressions of the world are not true is meaningless.

If this is right, then the skeptic is kidding himself if he thinks he can imagine that the only thing that exists is his own mind. He is kidding himself, because it couldn't be true that the physical world doesn't really exist, unless somebody could observe that it doesn't exist. And what the skeptic is trying to imagine is precisely that there is no one to observe that or anything else-except of course the skeptic himself, and all he can observe is the inside of his own mind. So solipsism is meaningless. It tries to subtract the extemal world from the totality of my impressions; but it fails, because if the extemal world is subtracted, they stop being mere impressions, and become instead perceptions of reality.

Is this argument against solipsism and skepticism any good? Not unless reality can be defined as what we can observe. But are we really unable to understand the idea of a real world, or a fact about reality, that can't be observed by anyone, human or otherwise?

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.


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