Sooner or later, all good dinner table debates reduce themselves to semantics. Yes, John Stuart Mill argued that your freedom only extends to the point where you do harm unto others, but what is harm? Sure, you can say that the Beatles were the best rock band of all time, but what do you actually mean by best? This kind of futile parsing is the raison d’être of Gary Saul Morson’s new book, a work devoted to the arcane matter of what is and isn’t a quotation.