…a Sign cannot denote an Object not otherwise known to its interpreter, for the obvious reason that if he does not already know the Object at all, he cannot possess those ideas by means of which alone his attention can be narrowed to the very Object denoted. Every object of experience excites an idea of some sort; but if that idea is not associated, sufficiently and in the right way with some previous experience, so as to narrow the attention, it will not be a Sign. A Sign necessarily has for its Object some fragment of history, that is, of the history of ideas. It must excite some idea.
—Charles S. Peirce, MS 849.9-10