The aim of this paper is to clarify Kierkegaard’s concept of demonic despair (and demonic evil) and to show its relevance for discussions of the guise of the good thesis (i.e. that in f-ing intentionally, we take f-ing to be good). Contemporary discussions of diabolic evil often emphasise the phenomena of despair and acedia as apparent counter-examples to the guise of the good. I contend that Kierkegaard’s analysis of despair is relevant to these discussions, because it reconciles demonic (extreme) despair (...) and acedia with the guise of the good. In The Sickness unto Death, Kierkegaard provides an influential, systematic account of despair that relates evil, despair, and acedia to each other. Michelle Kosch argues that this account goes beyond Kierkegaard’s German predecessors by introducing a concept of diabolic evil and despair. By contrast, the present paper argues that Kierkegaard takes diabolic evil to be impossible, although he offers a rich analysis of the demonic that resembles diabolic agency. Still, Kierkegaard’s analysis rests on ontological assumptions about the nature of the good that belong to a Platonico-Christian tradition that is controversial today. (shrink)