all allusions are references, but are all references allusions? Many people, following the advice of language critics, like to make a distinction between alluding to something and referring to it. By this thinking, allude and allusion should apply to indirect references in which the source is not specifically identified: “Well, we’ll always have Paris,” he told the travel agent, in an allusion to the movie Casablanca.

By contrast, refer and reference usually imply specific mention of a source: I will refer to Hamlet for my conclusion: As Polonius says, “Though this be madness, yet there is method in’t.” In practice, many writers do not follow this distinction, but it’s certainly worthy of consideration.