I cannot be sure that the world I take to be natural really is as it appears. Neither can I be sure that the categorial frame within which I experience it is any kind of absolute.
In principle this is both an epistemological and political stake in transcendental skepticism. Reality - not just the world as it appears but my very habits and chemical composition - is ideology.
Absolute knowledge is knowledge of transcendental skepticism - knowledge of the sheer astonishing power of the world to be otherwise. But it must be known in an embodied way - believed, loved, yearned for. Because it is also the sheer power of knowledge to be otherwise.