The German philosopher Martin Heidegger believed that human knowledge, at its most foundational and meaningful, is ineffable. Moreover, it requires stepping beyond what one sees as the established rules and into the realm of the unknown. Think of a master jazz musician or an elite athlete who, after facing an unpredictable moment, would find it impossible to convey precisely how and why they did what they did to deliver a peak performance.
Since Plato, a dominant strain of Western philosophy has understood human beings primarily as rational thinkers, a view typified by René Descartes's conclusion: cogito ergo sum ('I think, therefore I am'). But in 1927, the German philosopher Martin Heidegger radically upended this tradition in his monumental opus Being and Time. Thinking and theorising, he argued, presupposes a special mode of being that is unique to humans: I am, therefore I think.