The Nub of the Transcendental Aesthetic

The key thing to note in reading Kant is that here he makes absolutely clear just how radical his approach has to be. There must be a world behind appearances, that of which they are appearances, to which we never can have direct access. The world has to be there because otherwise the complexity of appearances would have no explanation, unless we assumed that all the appearances are a complicated video stream or a long-term hallucination. Barring this position there has to be a world beyond the world of appearances, and it also necessary that the world of appearances only becomes such a world because appearances are made possible by the presence of the pure a priori forms of intuition. Thus the world of appearances is entirely dependent on the forms that allow appearances to appear, and it is the presence of these forms that gives thinking or reason something to do, something to work on. 

Want to note here, which is the next step in our journey, that in order for appearances to be part of experience as objects the deliveries of intuition have to be remade by concepts. I do not mean that first we have red blobs and chunks of unprocessed time that we then make clear through reasoning. Rather, just as we always already experience things in time and space all that we experience is always already also thought, or categorized. or ordered using concepts.