Few philosophical theories are so hard to believe that no philosopher has ever defended them. But at least one theory is.
Suppose that you think lying is wrong. According to a view that is known as the error theory, you then take lying to have a certain feature: you ascribe the property of being wrong to lying. But the error theory also says that this property does not exist. This entails that lying is not wrong. You may therefore conclude that lying is permissible. But according to the error theory, you then ascribe the property of being permissible to lying. And the theory says that this property does not exist either. The error theory therefore entails that lying is neither wrong nor permissible. And it entails similar claims about anything else you could do.
Some philosophers have defended an error theory about moral judgements. But no one has so far defended an error theory about all normative judgements: all thoughts about rightness, wrongness, goodness, badness, reasons for action, reasons for belief, and so on. You may think that this is because such a theory is clearly false. But the arguments for this error theory are actually surprisingly strong. These arguments are not direct arguments for the theory, but are instead arguments against the alternatives to the theory: arguments against views according to which normative judgements are attitudes that do not ascribe properties, or views according to which the properties that these judgements ascribe do exist. When I consider each of these arguments on its own, I am convinced that it is sound. But when I consider all of them together, I am unable to form a belief in the theory they support: an error theory about all normative judgements.
Just as a theory can be true if we do not believe it, a theory can also be true if we cannot believe it.
What prevents me from doing this? When we have a belief, we cannot at the same time explicitly think that there is no reason whatsoever for this belief. For example, if we believe that Socrates was a philosopher, we cannot at the same time explicitly think that there is no reason whatsoever to believe that Socrates was a philosopher. If we did think this, our belief that Socrates was a philosopher would disappear. Since thoughts about reasons for belief are normative judgements, an error theory about all normative judgements entails that there is no reason to believe anything. It therefore entails that there is no reason to believe this error theory. And anyone who understands the theory well enough to believe it knows that it entails this. I think that this prevents us from believing this error theory.
You may take this to be a problem for the theory. But I do not think it is. Just as a theory can be true if we do not believe it, a theory can also be true if we cannot believe it. Of course, if we cannot believe a theory, we cannot sincerely say that it is true. But we can defend the theory without saying that it is true: we can put forward arguments against the alternatives to the theory and say that these arguments together seem to show that the theory is true. As long as we do not say that these arguments actually show this, we are not insincere. Moreover, if we did need to be insincere in order to defend this error theory, that would not be a problem for the theory. It would merely be problem for us.
So is this error theory true? Since I cannot believe the theory, I do not think it is. But I do think that the arguments against the alternatives to the theory together seem to show that the theory is true. And I think that our inability to believe an error theory about all normative judgements may explain why the philosophical debate about the nature of these judgements has been going on for so long without reaching a consensus: because we have been circling around a truth that we cannot believe.
Realising that we cannot believe this error theory may help us to make progress in this debate. And there may also be other philosophical theories that we cannot believe, such as scepticism about responsibility, eliminativism about belief, or nihilism about truth. If so, realising that we cannot believe these theories may help us to make progress in other philosophical debates as well.
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