Time is the formal a priori condition of all appearances. It has objective validity only in respect to appearances, not for things abstracted or taken in general. The empirical reality of time is not absolute reality. Time and space taken together, are the pure forms of all sensible intuition , and so are what make a priori synthetic propositions possible. The Transcendental Aesthetic cannot contain more that these two elements.
All intuition is nothing but the representation of appearances.
We cannot know the object itself. As appearances they cannot exist in themselves, but only in us. It is important that our Transcendental Aesthetic be certain, not just plausible. This also holds true of inner sense. This is not to say that these objects are mere illusion.