For the one says that you should philosophize about nature as if there were a necessarily first ground for everything belonging to existence, solely in order to bring systematic unity into your cognition by inquiring after such an idea, namely an imagined first ground; but the other warns you not to assume any single determination dealing with the existence of things as such a first ground,.e., as absolutely necessary, but always to hold the way open to further derivation and hence always to treat it as still conditioned.