For Jean Ladrière, a questioning of existential kind is a questioning on reason. Reason, revealing itself as it gets built up, is understood through the historical objectivities it implies. Yet, the study of the texts has shown that this movement of reason on itself rises a certain amount of aporias which only find their solution in more fundamental hermeneutics, that of existence. Though Ladrière does not specifically state the problems that arise with the conditions of hermeneutics from an ontological perspective, he still does understand them. If one can find in the distinction between constitué and événementiel the distinction between existentiell and existential, one still detects in Ladrière a kind of persistant subjectivism of which the origin may be questioned. There is in him a will to consider a subject that is admittedly not in charge of giving form to representations but that does not either firstly exist in the trial of its facticity. In this thesis work we attempted to answer the question of whether we should discuss a phenomenology or an hermeneutic ontology when dealing with Jean Ladrière.