Kant's immediate successors regarded Kant as having changed the course of philosophy. However, even during his lifetime, the intellectual world was torn by controversy over the meaning of his critical system. ‘Transcendental philosophy’ examines what Kant's contemporaries and later commentators took from his thoughts and how they analysed what he said. Was he really a Leibnizian? If the transcendental philosophy is not a version of Leibnizian rationalism, why is it not instead a repetition of the sceptical empiricism of Hume? Neither the Leibnizian nor the Humean interpretation is tenable. Kant's true critical philosophy can be assimilated to neither of its antecedents, since it removes the grounds from both.