Kant conceived of the task of securing the objectivity of knowledge as the challenge to establish the possibility of a priori knowledge. Not indeed of a priori knowledge tout court, but of a priori knowledge of objects, i.e. so-called synthetic a priori knowledge. If there is to be room for philosophical knowledge of the real beyond empirical science, then such knowledge must be possible independently of experience. In Kant's formulation of the problem in the Preface to the second edition of the Critique: