AbstractIf there is one lesson that Hannah Arendt drew from her encounter with Adolf Eichmann in Jerusalem it was that the moral and political dangers of thoughtlessness had been grossly underestimated. But while thoughtlessness clearly “has its perils”, (LMT 177) as the example of Eichmann illustrates, thoughtfulness has its own problems, as the example of Heidegger illustrates. In the course of her 1964 interview with Günter Gaus, Arendt recalls her distaste for “intellectual business” that arose from witnessing the widespread and “relatively voluntary” Gleichshaltung (co-ordination) of German “intellectuals” with the Nazis in 1933 (EU: 10). This was the year that Heidegger, Arendt’s former teacher and friend, “entered the Nazi Party in a very sensational way” (EU: 187). But Heidegger is for Arendt also a paragon of thoughtfulness who exposes the “incomprehensible triviality” (or banality) of “the they” and their “mere talk” (MDT: ix). This raises the following question: how can thoughtfulness, in the guise of Heidegger, and thoughtlessness, in the guise of Eichmann, both (though to a very different extent) lead to ‘co-ordination’ with the Nazis? What does this tell us about the relation between thinking and evil?