In "Being and Time" (1927), Heidegger undertook a "fundamental ontology" by analyzing Dasein - the human being for whom its own being is an issue - through structures of thrownness, care, and being-toward-death, arguing that confronting one's own mortality discloses the possibility of authentic existence against everyday absorption in the anonymous "they" (das Man). He argued Western philosophy since Plato had fallen into a "forgetting of Being" by conflating Being itself with particular beings.
Intellectual setting
Heidegger developed fundamental ontology as a radical extension and critique of his teacher Husserl's phenomenology, and his 1933 embrace of the Nazi party and rectorship of Freiburg University, along with his postwar silence about it, remain a central and unresolved controversy in the interpretation of his philosophy.
Key ideas
Being-toward-death and authenticity
Heidegger argued that Dasein's anticipatory confrontation with its own inevitable death discloses its existence as a finite, unrepeatable whole, opening the possibility of authentic existence in contrast to the evasive conformity of everyday absorption in "das Man," the anonymous they-self.
The forgetting of Being
Heidegger argued that the Western philosophical tradition since Plato had systematically conflated Being (the openness in which beings show up as intelligible at all) with particular beings, and that recovering the question of Being itself requires dismantling this inherited metaphysical framework.
Legacy
Heidegger is among the most influential and most contested philosophers of the twentieth century, directly shaping Sartre's existentialism, Gadamer's hermeneutics, and Derrida's deconstruction, while his Nazi involvement continues to provoke sustained critical reassessment of his legacy.