In the previous chapters, I have argued that neuroscience (and allied fields) can shed light on some of the perennial questions of moral theory and moral psychology: the nature of self-control and the degree to which agents should be held responsible for their actions. In this chapter, I explore another puzzle in moral psychology: the nature and existence of self-deception.

Self-deception is a topic of perennial fascination to novelists and everyone else interested in human psychology. It is fascinating because it is at once puzzling and commonplace. The puzzle it poses arises when we observe people apparently sincerely making claims that seem obviously false, and against which they apparently possess sufficient evidence. The man whose wife suddenly has many mysterious meetings, starts to receive unexplained gifts and is reportedly seen in a bar on the other side of town with a strange man has every reason to suspect her of infidelity. If he refrains from asking her questions, or is satisfied with the flimsiest of explanations, and fails to doubt her continued faithfulness, he is self-deceived. Self-deception is, apparently, common in the interpersonal sphere, but it is also a political phenomenon. Western supporters of Soviet communism were often, and perhaps rightly, accused of self-deception, when they denied the repression characteristic of the regime.

We say that someone is self-deceived, typically, when they possess sufficient evidence for a claim and yet continue, apparently sincerely, to assert the opposite.