One of the most striking themes in Raimond Gaita’s writings is his defence of the view that some thoughts are, and should be, unthinkable. To think some of these thoughts one would have to be either a crank or insane. To think others one would have to be evil. In making these claims Gaita is, characteristically, going against the general climate of opinion, especially among philosophers. But, equally characteristically, the defence of them is both deep and interesting. Since encountering his early development of these claims (in the ﬁrst edition of Good and Evil), I have been intrigued by them, with a mixture of enthusiasm and scepticism. Here I will brieﬂy outline Gaita’s account of what is unthinkable and then
defend enthusiasm for some of its components and scepticism about others. Whether or not the doubts about some parts are justiﬁed, the development of the view has been by any reasonable standard an important and serious contribution to ethics. Gaita discusses three kinds of thoughts that should be unthinkable. They
correspond to three kinds of people who might have them: people who are insane, people who are cranks, and people who are evil. The thoughts assigned in this context to the insane and to cranks purport to be factual. The thoughts assigned to evil people are moral or political. Gaita introduces the topic by discussing the ‘factual’ thoughts ﬁrst.