Because Rahner's superiors wished him to teach philosophy at Pullach, he returned home to Freiburg in 1934 to study for a doctorate in philosophy, delving more deeply into the philosophy of Kant and Maréchal, and attended seminars by Martin Heidegger. His philosophy dissertation "Geist in Welt", an interpretation of Aquinas's epistemology influenced by the transcendental Thomism of Maréchal and the existentialism of Heidegger, was ultimately rejected by his mentor Martin Honecker, allegedly for its bias toward Heidegger's philosophy and not sufficiently expressing the Catholic neo-scholastic tradition. In 1936 Rahner was sent to Innsbruck to continue his theological studies and there he completed his "habilitationsschrift". Soon after he was appointed a "Privatdozent" (lecturer) in the faculty of theology of the University of Innsbruck, in July 1937. In 1939 the Nazis took over the University and Rahner, while staying in Austria, was invited to Vienna to work in the Pastoral Institute, where he both taught and became active in pastoral work until 1949. He then returned to the theology faculty at Innsbruck and taught on a variety of topics which later became the essays published in "Schriften zur Theologie (Theological Investigations)": the collection is not a systematic presentation of Rahner's views, but, rather a diverse series of essays on theological matters characterised by his probing, questioning search for truth.