Heidegger

Heidegger's Being and Time (1927) is the long question: what does it even mean for anything to be? Western philosophy, from Plato onward, had taken being for granted while obsessing over particular beings. Heidegger's project was to wake up the question.

The method is phenomenology — describe the structures of experience as they actually present themselves — but Heidegger pushes it toward fundamental ontology. He starts not with a disinterested subject contemplating objects, but with Dasein: the being for whom being is a question. That's us. We don't first encounter the world as a collection of objects, then add meanings; we encounter it always already meaningful, organized by our concerns and projects. A hammer isn't first a lump of stuff plus the property "for hammering"; it's zuhanden — ready-to-hand, embedded in a workshop of involvements. Only when it breaks does it become vorhanden — present-at-hand, the bare thing we then theorize about.

The book's other monument is Heidegger's analysis of authenticity. Most of the time, we live as "das Man" — the They, the impersonal anyone — borrowing our opinions, tastes, even our anxieties from the public sphere. Authenticity is the rare move of facing our own being-toward-death and choosing our possibilities as our own. The framework runs through Sartre, the entire existentialist tradition, and a lot of twentieth-century theology.

Then there's the Nazi problem. Heidegger joined the Nazi party in 1933 as rector of Freiburg, gave speeches in line with the regime, and never explicitly recanted. The Black Notebooks (released starting 2014) contain unmistakable antisemitism. How much this contaminates the philosophy is a serious, ongoing debate — split roughly between those who think the work survives quarantining the man and those who think the philosophy itself contains the seeds of what he chose.

Later Heidegger (the Letter on Humanism, The Question Concerning Technology) shifts toward a more poetic, meditative idiom about language as "the house of Being." Influential on Derrida, Gadamer, much of continental philosophy.