Ambiguity

One of the characteristics of any language is ambiguity. Ambiguity means that an utterance can have more than one interpretation. For instance, there's lexical ambiguity ("Replace the pencil," can mean "Put the pencil back," or "Take the pencil away and put another in its place.") Or, there's structural ambiguity (The classic example from Chomsky is "Visiting relatives can be tedious.") Finally, there's situational ambiguity (A letter of reference that says, "You will be lucky if you can get him to work for you.")
In some situations, such as legal documents, ambiguity is disastrous. In others, it can be funny, intentionally or otherwise. For instance, I come into my children's' bedroom and see feather pillows all over the place. I say, "Well, aren't we being good." The situation is strictly speaking, ambiguous, since the sentence can be taken one of two ways: as sincere or as sarcastic. Generally, things like the situation and voice tone can disambiguate the sentence.
One of the interesting things about ambiguity is that when we run across it we don't normally recognize it as ambiguity. Instead, we choose one of the interpretations and simply go with it. Take another sentence from Chomsky: "The shooting of the hunters was terrible." People will choose one or the other of the meanings (but you got them both, right?) and not even see the other one. So strong is this tendency that some people can't see the ambiguity until it is carefully pointed out to them. I've always thought that the ability to see ambiguity is both a blessing and a curse.