『Being and Time』要約

Martin Heidegger’s *Being and Time*, published in 1927, is a foundational work of existential phenomenology and one of the most influential philosophy books of the twentieth century. Its central aim is to reopen the question of the meaning of Being, which Heidegger argues has been forgotten by the Western philosophical tradition since Plato and Aristotle. He begins by analyzing the one entity that asks this question: human existence, which he calls Dasein, or “being-there.” Heidegger’s method is phenomenological, examining how Dasein actually exists rather than treating it as a detached Cartesian subject. Dasein is defined by “being-in-the-world,” meaning it is always already engaged with a meaningful world of tools, projects, and other people. This everyday involvement is contrasted with theoretical detachment, which Heidegger sees as derivative. He describes the “ready-to-hand” (equipment) and the “present-at-hand” (objects of mere observation), showing how things appear differently depending on our practical attunement. A major portion of the book analyzes temporality as the horizon for understanding Being. Heidegger argues that Dasein is fundamentally temporal: it exists as a projection into possibilities while always already thrown into a situation. Authentic existence involves confronting one’s own finitude—being-toward-death—rather than fleeing into the impersonal “they-self” of idle talk and curiosity. Anxiety, rather than fear, discloses this groundlessness. The work famously remained incomplete; its projected second half, which would have addressed Being itself beyond Dasein, never appeared. Its dense vocabulary and unfinished structure have made it a lasting source of debate in continental philosophy.