We take it for granted that anyone can understand a story. But every kind of narrative demands some listening skills. Even the best storytellers find it hard to entertain children, who are prone to interrupt with questions that make perfect sense by themselves but drift away from the story's theme. Where does Mary live? Does she have a dog? To listen well, a child must acquire potent forms of self-control.
The storyteller, too, must work to fix the focus of the listener's mind. If you were speaking about something else and suddenly, completely out of context, remarked, Mary was invited to Jack's party, an unprepared listener might wonder, Mary who? and look to see if you were addressing someone else. But you can first prepare the listener by saying, Would you like to hear a story? or simply, Once upon a time . . . What is the function of such a phrase? It has a very specific effect: to set the listener into a normal and familiar state of expecting to hear a certain type of narrative — a story. In the English tradition, stories typically begin by specifying the time — if only vaguely, by saying long ago. I'm told that in Japan most stories start with saying where as well — if only by some empty phrase like in a certain time and place. The biblical book of Job begins with, There was a man in the land of Uz . . .
Most stories start with just enough to set the scene. Then they introduce some characters, with hints about their principal concerns. Next, the storyteller gives some clues about some main event or problem to be solved. From that point on, the listener has a general idea of what comes next: there will be more development of the problem; then it will be resolved, somehow; and then the story will end, perhaps by giving some practical or moral advice. In any case, those magic story-starting words arouse, in knowing listeners' minds, great hosts of expectation-frames to help the listeners anticipate which terminals to fill.
Beyond arousing all these specific expectations, once upon a time plays one more crucial role: it says that what comes after it is fictional or, in any case, far too remote to activate much personal concern. Instead, it tells the listener to disregard the normal sympathies one should feel when real persons meet the monstrous destinies so usual in children's tales: to be turned into toads, imprisoned in stones, or devoured by terrible dragon beasts.