The consciousness of ignorance- unless this ignorance is recognized to be absolutely necessary ought, instead of forming the conclusion of my inquiries, to be the strongest motive to the pursuit of them.
All ignorance is either ignorance of things or of the limits of knowledge.
In other words, our empirical knowledge is limited by that which yet remains for us to know. If I regard the earth, as it really appears to my senses, as a flat surface, I am ignorant how far this surface extends. The sum of all the possible objects of our cognition seems to us to be a level surface, with an apparent horizon- that which forms the limit of its extent, and which has been termed by us the idea of unconditioned totality. To reach this limit by empirical means is impossible, and all attempts to determine it a priori according to a principle, are alike in vain. But all the questions raised by pure reason relate to that which lies beyond this horizon, or, at least, in its boundary line.