But let it be considered that hardly any thing can strike the mind with its greatness which does not make some sort of approach toward infinity; which nothing can do while we are able to perceive its bounds; but to see an object distinctly, and to perceive its bounds, are one and the same thing. A clear idea is, therefore, another name for a little idea.
(Edmund Burke, A Philosophical Inquiry into the Origin of Our Ideas of the Sublime and the Beautiful, Part II, Section V.) Inquiry into the sublime, then, is inquiry into ideas that cannot be made clear and distinct, not from any defect in the idea, but from inadequacy in the human mind: sublime ideas are ideas that cannot be made wholly clear because they are inexhaustible, infinite in at least a loose sense, and there is too much to them. To use the Cartesian metaphor, they are mountains, and while your mind can touch them it cannot encircle them. And the subject is in part interesting because neither the 'rationalists' nor the 'empiricists' in the early modern period had tools that were obviously adequate for an account of such ideas. When Kant looks into the question of the sublime in the Critique of Judgment, he is not merely taking an idle interest in a question that people were interested in at that time, any more than his discussion of teleology is just the expression of an idle interest in design arguments. It's a matter of considerable epistemological moment; a failure to include the sublime would be a serious deficiency in the account, an open invitation for all sorts of errors. When the Romantics occasionally put great emphasis on the sublime, it is also not a mere expression of their interest in aesthetics; it is simultaneously a critique of alternative philosophical movements and at the heart of a movement for re-thinking our entire approach to philosophical questions. It even pops up in places you might not expect: Darwin, for instance, rightly recognizes that evolution is a sublime idea in the technical sense, and (in the notebooks especially) this fact occasionally is found as part of a criticism of some of his opponents: contrary to what they themselves would think, their world is small, a world without grandeur that has a God without sublime power and dignity, a world and a God that can be parsed entirely by little ideas. Evolution, on the other hand, as in the evolution of the eye, is something that reason can recognize in its general sweep but whose infinities -- countless little variations in countless steps over mind-bogglingly long ages -- exceed all imagination.
But what often strikes me when I look around at the philosophical scene today is how foreign this has all become. There are a few exceptions, but sublimity has vanished as a serious concern. We too live in a world of little ideas, or presumed to consist of nothing but little ideas. The danger of that, of course, is that it is a breeding ground for intellectual hubris at precisely the points where all our interests are most parochial.