The four sections of the Metaphysische Anfangsgründe der Naturwissenschaft ¹ are each introduced by a new definition of matter. For the Phoro nomy it is defined as the movable in space (Ak. IV, 480); the other definitions presuppose this one. What is the status of the propositions ascribing existence to matter in these senses? Are the metaphysical principles of natural science as pure as the principles of pure understanding, or are they only required for experience which happens, in fact, to contain matter as defined at the beginnings of the sections?