Phenomenology, as we will consider it, begins with the work of Edmund Husserl in the first three decades of the twentieth century. Its descendants include existential phenomenology, associated with Husserl's pupil, Heidegger – whose opacity makes Husserl look almost a paragon of clarity in comparison – and existentialism itself. Within the broad existential tradition the work of the French philosopher Maurice Merleau-Ponty has become recognized as important to present-day constructionist concerns in the broad sense. One of its other descendants, the social phenomenology of Alfred Schutz, has been a direct influence upon ethnomethodology, and thence discourse analysis in the broad sense. In addition, Schutz's legacy is centrally important in one of the founding documents of contemporary social constructionism, Berger and Luckmann's (1966) volume The Social Construction of Reality (Luckmann being a co-author with Schutz of The Structures of the Life-World (1973–89). Schutz grasped the principles of phenomenology sufficiently well to have been offered the position of Husserl's assistant in the 1920s (an offer he turned down). He notes that: