Carl Schmitt

Schmitt is read by left and right because his definitions are so sharp: "Sovereign is he who decides on the exception" (Political Theology, 1922), and politics itself is the distinction between friend and enemy (The Concept of the Political, 1932). Both books are short and bear on every debate about emergency powers and polarisation. They come with a serious warning: Schmitt joined the Nazi Party in 1933 and justified Hitler's purges, and his critique of liberal parliaments was written to be used.