The physicist Carl Friedrich von Weizsäcker recounted a walk in the Black Forest with Martin Heidegger. The pair came to a halt on a thick patch of damp moss. Weizsäcker pointed out that the path had come to an end. The philosopher looked at him “craftily” and explained: “It is a holzweg, it leads to the sources [er führt zu den Quellen]. Of course I didn’t put that in the book.”1 Heidegger cou...