“If Gertrude and Ludwig had ever met, apparently they could have talked for hours about the sixth Act IV of An Exercise in Analysis (1917). The act in its entirety is: ‘Now I understand.’ This is the sort of statement that worried Wittgenstein for the last thirty years of his life. It involves the problem of other minds, of certainty, of epistemology, and the language game. We can supply many contexts for such a statement.”

(Guy Davenport, “Late Gertrude”, p. 189 in The Hunter Gracchus.)