Heidegger is unique in the history of modern philosophy in describing the phenomenon of thought, which makes humans unique and appropriate to be given the phenomenological designation of Dasein in Being and time, when there is every danger of reducing thought to reason while philosophers work against the background of the Enlightenment tradition that is handed down to them. In Being and time, Heidegger introduces the notion of Stimmung to encompass the complex activity of thought.