MARVELS REPRESENT MOMENTS when we encounter something unexpected or unfamiliar—invisible forces take visible forms, and the impossible intersects with the quotidian. Historical approaches classify medieval marvels as natural or demonic based on the agency behind them; in Richard Kieckhefer's formulation, “demonic magic invokes evil spirits and rests upon a network of religious beliefs and practices, while natural magic exploits ‘occult’ powers within nature and is essentially a branch of medieval science.” Literary texts focus on the effect rather than the agency: something is marvellous because it inspires marvel. Caroline Walker Bynum has demonstrated that “medieval theorists […] understood wonder as cognitive, non-appropriative, perspectival, and particular.” We can find similar characteristics in the responses to literary marvels, and examining those reactions can open up insights about the texts, characters, and readers; a shared definition of what is marvellous may identify a community, for example, or map the boundaries of moral behaviour.

In Chaucer's works, merveille is connected with a range of elements—secular and religious, human and supernatural, public and private. Three tales that usually appear near the middle of the Canterbury Tales, albeit in different orders in different manuscripts, explore key aspects of the marvellous. The Squire's Tale offers marvels that are public and supernatural (typical characteristics of literary marvels during the later Middle Ages), and attends carefully to the reactions of the witnesses. In the Franklin's Tale, the marvels fall on the border between supernatural and natural; they are still visual spectacles, but their impacts within the text are more personal. The marvels in the Clerk's Tale are significantly not supernatural but instead focused on human behaviour and how extreme it can become. Across these three texts, marvels raise moral questions about how we understand ourselves, how we define our communities, and how we treat others.

Merveille often appears alongside related words like wonder or miracle. Chaucer chooses wondermost frequently, including as an adverb (making an action or characteristic more distinctive or intense, as when Palamon and Arcite fight “wonder longe” in the Knight's Tale, 1.1654) and as a noun in the phrase “no wonder” (which appears about twenty times across his works).