Our reader must be anxious to know what finally became of Mary and that kite. Here is more of that story.
Mary was invited to Jack's party. She wondered if he would like a kite. Jane said, Jack already has a kite. He will make you take it back.
What does the pronoun it mean here? Clearly Jane is speaking not of the kite that already belongs to Jack, but of the new kite that Mary is thinking of giving to him. But what leads the listener to assume that this is what the storyteller meant? There are many issues here besides the question of which kite is involved. How do we know it refers to a kite at all? Does take it back mean take it back from Jack or to return it to the store? For the sake of simplicity, let's put aside the other possibilities and assume that it must mean a kite. But in order to decide which kite is meant, we still must understand the larger phrase take it back. This phrase must refer to some structure already in the listener's mind; the narrator expects the listener to find the appropriate structure by activating an appropriate fragment of commonsense knowledge about giving and receiving birthday presents. But since every listener knows so many things, what sorts of processes could activate the appropriate knowledge without taking too much time? In 1974 Eugene Charniak, a graduate student at MIT, asked how each phrase of this story works to prepare the reader to comprehend the subsequent phrases. He suggested that whenever we hear about a particular event, specific recognition-agents are thereby aroused. These then proceed actively to watch and wait for other related types of events. (Because these recognition-agents lurk silently, to intervene only in certain circumstances, they are sometimes called demons.) For example, whenever a story contains the slightest hint that someone may have purchased a gift, specific demons might be aroused that watch for events like these:
If there is evidence that the recipient rejects the gift, look for signs of it being returned. If you see evidence of a gift being returned, look for signs that the recipient rejected it.
Charniak's thesis raised many questions. How easy should it be to activate demons? How long should they then remain active? If too few demons are aroused, we'll be slow to understand what's happening. But if too many become active, we'll get confused by false alarms. There are no simple solutions to these problems, and what we call understanding is a huge accumulation of skills. You might understand certain parts of a story by using separate, isolated demons; you might comprehend other aspects of that same story by using larger-scale processes that try to match the sequence of events to various remembered scripts; yet other understandings might depend upon which agents are aroused by various micronemes. How much of the fascination in telling a story, or in listening to one, comes from the manipulations of our demons' expectations?