I was getting at that it denotes the sphere of posssibility not the world, the wolrd is different idea for Kant and is at the centre of his project. His philosophy project is trying to continue the projects of his time (Baumgarten and Wolff) and in Wolff he sees the ultimate failiure of philosophy as he can't ground the concept of the world (no totality of space/time just singular things, which for Kant means a problem with scientific principles). Another point, based on my own work not general scholarship, is that the negation/affirmation/limitation is paradigmatic here, and we see very explicitly the conditions of transcendental philosophy as the necessity of separating limitation and negation that in non-critical philosophies coincide and concerns infinite judgments (judgments where the predicate includes negation). The procedure of transcendental philosophy is like logic but without abstracting from content, by analysis of necessary conditions and limitation of speculation that precludes judgments from deducing A from non-A because of transcendental aesthetics. So to come back to the categories, there is the infinite space of possible predicates of soul (each subject of judgment gets its own infinity, this is analysis of term logic) and we have the predicate 'mortal' excluded from it, this negation does not negate the infinity of possible predicates of the soul, so our knowledge of the soul remains the same (no apophatic theology). This has to do with the knowledge of things in themselves, not the universe/the world.