Kant's phrase "transscendentale Einheit der Apperception" translated as "transcendental unity of apperception" seems to say it all, that whatever is experientially known in any way presupposes a prior field of knowing, an awareness without any content of its own in which everything arises, and yet it is commonly understood via the (posterior) idea that "I think" can be appended to any experience without modifying it. This treats it as if its acknowledgment is optional. In phenomenology the transcendental field is accessed by performing a special kind of mental act that takes you out of the "natural attitude", as if on holiday away from home, as if it were not the so-called natural attitude that was the result of adding something extraneous to the truly natural transcendental consciousness. This ought to be how it goes, that once you grasp what is at stake in transcendental consciousness you are back home in it for good, and the natural attitude loses its ability to keep you tied into a distinctly unnatural set of implicit assumptions. Admittedly, it very hard to speak properly, that is, without circularity or self-contradiction, of that prior awareness to which Kant's phrase so felicitously points.