The Inconsistent Triad
An inconsistent triad is a set of three claims that cannot all be true at the same time.
In the case of skepticism, the triad looks like this:
| Proposition | Negation |
|---|---|
| I cannot be sure that I am not a brain in a vat. | I can be certain that I am not a brain in a vat. Either there are certain properties about my experiences that allow me to be certain, or I can use reason to prove it. |
| If I cannot be sure that I am not a brain in a vat, then I cannot know anything about the external world. | For me to know something about the external world, I do not need to be certain that I am not a brain in a vat. |
| I can know something about the external world. | I cannot know anything about the external world. This is the global skeptic’s position. |
The Skeptical Problem
The skeptic argues that if I cannot rule out skeptical scenarios, such as being a brain in a vat, then I cannot know anything about the external world.
For example, I might think I know that:
- I have hands
- I am sitting in a room
- There are other people around me
- The world existed before I was born
- The sun will rise tomorrow
But if all of my experiences could be produced while I am merely a brain in a vat, then perhaps I do not really know any of these things.
Questions
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Which of the three negations above do you believe?
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How do I know that I am not dreaming or hallucinating?
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What sorts of things do I need in order to know something?
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Is there any way science can help us out of this mess?
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Even if you do not believe the skeptic’s argument for all external knowledge, you might believe it for some things. Which kinds of things can we know? Facts about the future? The past? Places not currently in our sensory experience?
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Even if the skeptic’s argument is a good one, we do not usually go around acting like we know nothing about the external world. What would the world be like if we did take the skeptic’s arguments as true? Would it be a better world? A worse world? Is it good always to be in doubt? Is there something comforting about the fact that you might be wrong?