Heidegger wrote his qualifying dissertation on Duns Scotus in 1915. In this original work, he discusses the doctrine of categories of Duns Scotus in relation to his doctrine of meaning. Heidegger uses the modern logic of Edmund Husserl and Emil Lask to interpret a scholastic treatise that was, as was later proven, not written by Scotus himself, but his pupil, Thomas of Erfurt. At the same time, he uses the medieval doctrine of categories and meaning to criticize contemporary theories. The great advantage of Scotus’ doctrine over modern logic is its metaphysical foundation. As Heidegger writes in his final chapter, which is a later addendum to the published edition of 1916, “in the long run philosophy cannot do without its optics metaphysics.” Heidegger’s original approach to philosophy and its history brought him to the attention of Paul Natorp, who, in 1923, would play a pivotal role in Heidegger’s appointment as a professor at the University of Marburg.