Martin Heidegger (/ˈhaɪdɛɡər, -dɪɡər/; German: [ˈmaɐ̯tiːn ˈhaɪdɛɡɐ]; 26 September 1889 – 26 May 1976) was a German philosopher and a seminal thinker in the Continental tradition, particularly within the fields of existential phenomenology and philosophical hermeneutics. From his beginnings as a Catholic academic, he developed a groundbreaking and widely influential philosophy.
His best known book, Being and Time (1927), is considered one of the most important philosophical works of the 20th century. In it and later works, Heidegger maintained that our way of questioning defines our nature. He argued that Western thinking had lost sight of being. Finding ourselves as "always already" moving within ontological presuppositions, we lose touch with our grasp of being and its truth becomes "muddled". As a solution to this condition, Heidegger advocated a change in focus from ontologies based on ontic determinants to the fundamental ontological elucidation of being-in-the-world in general, allowing it to reveal, or "unconceal" itself as concealment.