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Bart Streumer defends an error theory that suggests that all moral and other normative judgements are false; and then he argues that we cannot believe this theory. But this need not be a problem: Streumer holds that to make philosophical progress, we need to make a sharp distinction between a theory´s truth and our ability to believe it.

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Unbelievable Errors defends an error theory about all normative judgements: not just moral judgements, but also judgements about reasons for action, judgements about reasons for belief, and instrumental normative judgements. This theory states that normative judgements are beliefs that ascribe normative properties, but that normative properties do not exist. It therefore entails that all normative judgements are false.

Bart Streumer also argues, however, that we cannot believe this error theory. This may seem to be a problem for the theory. But he argues that it makes this error theory more likely to be true, since it undermines objections to the theory and it makes it harder to reject the arguments for the theory.

He then sketches how certain other philosophical theories can be defended in a similar way. He concludes that to make philosophical progress, we need to make a sharp distinction between a theory´s truth and our ability to believe it.

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Bart Streumer´s Unbelievable Errors is an outstanding defense of the error theory - the theory that all normative judgments are false. It is exceptionally well written and thorough and breaks new ground in its argument that our inability to believe the error theory makes the theory more likely to be true. Those interested in the error theory and metanormative debate more generally cannot afford to miss this book. St. John Lambert, Ethics

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Bart Streumer is Professor of Philosophy at the University of Groningen. He previously taught at the University of Reading. His work on metaethics has appeared in the Journal of Philosophy, Philosophical Studies, and the Australasian Journal of Philosophy.

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