And suppose a teacher is teaching a number of beginners to read. Some pretend, others occasionally get it right by accident, others have already learned to read. When has someone passed into the latter class? In general, there will not be an identifiable moment when this has happened: the teacher will judge of a given pupil that he has ‘learned to read’ if he passes tests for reading often enough. There may or may not be an identifiable moment when the pupil first felt, ‘Now I am reading!’ but the presence of such an experience is neither a necessary nor a sufficient condition for the teacher to judge of him that he is reading.
Saul A. Kripke, Wittgenstein: On Rules and Private Language