Ambiguity is the condition that results when the denotative process yields an unexpected, alternate meaning. The new critic William Empson devoted an entire book (called Seven Types of Ambiguity) to cataloguing this effect. When ambiguity seems intentional, as is often the case, we might appraisingly call it “polysignation,” and nod approvingly. When it’s funny, we call it a “pun” or “paronomasia.” Here is an exemplary paronomasiac couplet from Alexander Pope’s mock-epic The Dunciad: “Where Bentley late tempestuous wont to sport / In troubled waters, but now sleeps in port.” “Port” in this couplet refers first to a harbor for ships to dock, and is summoned by “troubled waters”; but port is also a double-fortified sweet wine, and “sleeps in port” has a comically derogatory other meaning (he’s passed-out drunk, ha ha ha).
But ambiguity can also seem irregular, discomfiting, contrary to sense, unintentional, and/or problematic. The more pressure you put on the syntax and diction of any particular passage, the more likely it will seem to you that the normal denotations of a text may yield up alternate meanings; this is a normal function of close reading. In all cases follow the advice for the “affective fallacy”; decide for yourself whether the alternate ambiguous constructions are sponsored by the text, or are the results of your close attentions. If the alternatives seem apt, then try to read the text as if both meanings are summoned for the reader at once: we call these nuances and resonances. It is sometimes a function of language rather than the individual text’s apparent project; but in any case remember it’s only the task of the new critic to test the text to see what meanings are present, not to account for the authorial intention.
One last thing about ambiguity: if you look up the dictionary definition for the term, you’ll see that it has a root in “ambi—” meaning “both” rather than “two.” Two options present themselves, and the careful reader attends to both at the same time. Even if the context allows you to drop one eventually, the alternate reading still lingers in the background and ought to inform your interpretation. At any rate, for the purposes of literary study, you should assume that the text you are reading is an intentional thing: that resonances and nuances attend language because that’s what happens with language, rather than because the author goofed. So do not confuse “ambiguity” with vagueness or incompetence. Use it instead to identify places where the instability of language is storing up energy by housing simultaneous meanings; also, it’s an instance of a text signaling to you that you should pay attention, because this is a crucial detail.