He completed his doctoral thesis on psychologism in 1914, In the two years following, he worked first as an unsalaried Privatdozent.
He served as a soldier during the final year of World War I, working behind a desk and never leaving Germany.
When Husserl retired as Professor of Philosophy in 1928, Heidegger accepted Freiburg's election to be his successor, in spite of a counter-offer by Marburg.
According to the Internet Encyclopedia of Philosophy, he is "widely acknowledged to be one of the most original and important philosophers of the 20th century." Heidegger is best known for his contributions to phenomenology and existentialism, though as the Stanford Encyclopedia of Philosophy cautions, "his thinking should be identified as part of such philosophical movements only with extreme care and qualification." In the first division of the work, Heidegger attempted to turn away from "ontic" questions about beings to ontological questions about Being, and recover the most fundamental philosophical question: the question of Being, of what it means for something to be.
Heidegger approached the question through an inquiry into the being that has an understanding of Being, and asks the question about it, namely, Human being, which he called Dasein ("being-there").
He helped Blochmann emigrate from Germany before the start of World War II and resumed contact with both of them after the war.
Heidegger spent much time at his vacation home at Todtnauberg, on the edge of the Black Forest.
Heidegger also made critical contributions to philosophical conceptions of truth, arguing that its original meaning was unconcealment, to philosophical analyses of art as a site of the revelation of truth, and to philosophical understanding of language as the "house of being." Heidegger's later work includes criticisms of technology's instrumentalist understanding in the Western tradition as "enframing," treating all of Nature as a "standing reserve" on call for human purposes.
Heidegger is a controversial figure, largely for his affiliation with Nazism, as Rector of the University of Freiburg for 11 months, before his resignation in April 1934, for which he neither apologized nor publicly expressed regret, Raised a Roman Catholic, he was the son of the sexton of the village church that adhered to the First Vatican Council of 1870, which was observed mainly by the poorer class of Meßkirch.
His family could not afford to send him to university, so he entered a Jesuit seminary, though he was turned away within weeks because of the health requirement and what the director and doctor of the seminary described as a psychosomatic heart condition.
Heidegger was short and sinewy, with dark piercing eyes.
He also read the works of Dilthey, Husserl, and Max Scheler.
In 1927, Heidegger published his main work Sein und Zeit (Being and Time).
The consequence of this is that our capacity to think cannot be the most central quality of our being because thinking is a reflecting upon this more original way of discovering the world.