Ways around skepticism I: Verificationism

I want to consider now a view of knowledge that was very influen­tial in the twentieth century and that seems to offer a way out of the skeptical impasse.

Since we are usually concerned with states of affairs that we can discuss in our language, verificationists usually express their posi­tion in terms of the sentences that describe states of affairs. Sentences that describe states of affairs and can therefore be true (if the state of affairs is as they say it is) or false (if it is not) we can call declarative sentences. They declare how the person who says them believes the world to be. So we can express verificationism like this:

V: For every declarative sentence, there must be some sort of evidence that would provide grounds either for believing or for disbelieving it.

A sentence for which there is the possibility of evidence—either for or against—is called a verifiable sentence. Every declarative sentence, the verificationist says, must be verifiable. This thesis, which we call the verification principle, is a radical version of empiricism—radical because it says, in effect, that every sentence that makes a claim about the world has to be subject to the evidence of experience. Indeed, the Austrian philosopher Moritz Schlick, who was one of the leaders of the school of philosophy called logi­cal positivism, which developed verificationism, called his view “consistent empiricism.” But on the face of it, the verification prin­ciple seems to assume that the universe is arranged for our episte­mological convenience.

The best argument for the verification principle depends on some assumptions about language, which we shall be discussing in more detail in the next chapter. But I will outline the basic argument here:

For our sentences to have meanings, there must be rules for how we use them.

A sound that you use without following any rule at all cannot be a meaningful sentence. A rule for a sentence will say when you should use it and when you should not. For example, the rule for using the sentence “I am hot” is, roughly, that you should use it when you want to communicate the fact that you are hot, and not otherwise.

One way to defend a position is to show by reductio that it is wrong to deny that position. If we can show that denying a claim leads to a conclusion we can recognize as false, then the claim itself must be true. So let's suppose that the verification principle, V, is false, and see if that leads to a false conclusion.

Suppose, then, that there could be a declarative sentence, S, that you could not in any circumstances find evidence for or against. So, of course, there would be no circumstances in which you could use it. But then there would be no rule that said under what circumstances you should use it and under what other circumstances you should not. But since, as I said, every sentence that is meaningful must be used in accordance with some rule, it follows that there cannot be a meaningful sentence like S.

Some argument of this sort led many philosophers to accept verifi- cationism. Verificationism says that the only reality we can mean­ingfully talk about consists of things that people are capable of detecting.

There are two important things to notice about this argument for verificationism. First, it doesn't show that we must actually be able to find evidence for or against every declarative sentence. A rule must establish circumstances in which the sentence would be prop­erly used. But for there to be a rule it does not have to be possible for us actually to get into one of those circumstances. I am not able to get to the nearest star, and I don't know how to measure the tem­perature of remote objects. But there is a perfectly good rule for when to use the sentence “The nearest star is hot”: use it when you want to communicate the fact that the nearest star is hot. This is a sentence that you could have evidence for if you traveled 4.3 light- years to Proxima Centauri with a thermometer, even if you can't actually get there now. It follows that if the verification principle is supported by this argument, we must interpret it as requiring that it should be possible for someone, somewhere, sometime to have gath­ered evidence for or against every declarative sentence, not as requiring that it should be possible for you or me to find evidence here and now.

That brings us to the second important thing to notice about the argument, which is that it does not assume that the universe is organized for our epistemological convenience. The argument I have given depends on assumptions about what our language must be like, not on assumptions about what the universe must be like.

Consider any property, P, about which we have beliefs. For P to play any part in our lives we must be able to conceive of circum­stances in which we would apply it. Call such circumstances P's “cir­cumstances of ascription.” Under a property's circumstances of ascription, a suitably situated observer may interact with the prop­erty in ways that give him or her knowledge that it obtains. Even if we don't actually know whether anything has this property, we can still imagine that if anything does have it, someone could have known this if its circumstances of ascription had obtained and if they had been in a position to perceive the circumstances of ascription. It follows that we cannot possess the idea of any property that no one could in any circumstances have known to hold.

This argument should be particularly appealing to someone who believes that the kind of functionalism I described in the last chap­ter is correct. For, if functionalism is correct, then for each belief there should be a way of saying what its functional role is, a way of saying what role it plays in determining what people with that belief will do in response to the experiences they have. But if it is impos­sible for anyone to come to believe that something has the property P, then the belief that something is P has no functional role: there are no experiences that would cause the person with that belief to do anything.

This line of thought might, if suitably elaborated, lead you to accept a version of verificationism: one that said that every property in a certain class must be one that could be known under some cir­cumstances to obtain. A similar line of thought would lead to the view that every name must have circumstances in which some agent could know that the thing it named had some property.

If this argument is sound, we have reason to believe that the behaviorists and the functionalists were right to deny that there could be essentially private mental states.

Verificationism not only provides grounds for rejecting Cartesian philosophical psychology but also offers an answer to skepticism. The skeptical hypotheses of the evil demon and the brain in the vat are both designed to raise the possibility that there are states of affairs that no amount of evidence could detect. But the verification principle says that no sentences that purport to describe unde­tectable states of affairs can be meaningful, and the argument I have just offered is intended to show that nobody can have beliefs about undetectable states of affairs. So if the verification principle is cor­rect, skepticism will not be a real possibility, because the skeptical stories literally will not make sense.

But because we started with the story of Albert, the brain in the vat, the verification principle is likely to seem implausible. Albert was unable to tell the difference between the following two hypotheses:

a)     that he was moving around in the world having experiences of real things; and

b) that he was a brain in a vat with faked experiences.

And the story seems to make perfect sense. If it does make sense, it seems to be a clear case of something that the verificationist says is impossible: an issue that no evidence could decide.

But is it really a case that the verificationist should accept as a counterexample? For example, suppose Marie found a new body for Albert. Couldn't she then reconnect him to his body and tell him that his experiences since the crash were all faked? And wouldn't he then have evidence that he used to be a brain in a vat? Of course, Albert has no control over whether Marie does provide him with this evidence.

Verificationism doesn't help as a solution to skepticism. The skep­tics want a way of checking whether their experience is misleading them, not the reassurance that evidence that they are being misled could eventually show up. And if verificationism is correct, it offers only this weaker sort of reassurance.

But another way out of skepticism has been suggested recently. This new approach was prompted by a class of examples that under­mined the long-established principle of deduction for justification.

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