The literary device of “Allusion” is explained by John Sutherland in his clear inimitable style: ‘Works of literature, we should realize, are not islands, entire of themselves. They connect with other works – invisibly and visibly. The most visible, controlled and knowing form of connection (other than outright plagiarism) is allusion.’ Then he describes how it differs from other kinds of literary reference: ‘It may look like what theorists like to call “intertextuality” […] but allusion quacks rather differently. It is not a genetic thing – like shared DNA – but a device, a tool, effectively, with which the author can do interesting things and create interesting effects.’ T. S. Eliot in The Waste Land ‘ uses allusion as a framework’. His famous poem opens with a description of April as ‘the cruellest month’, an allusion to Chaucer's Canterbury Tales, which in turn alludes to Petrarch, who in turn alludes to a genre of poetry celebrating spring and birth. Sutherland concludes: ‘Eliot is asserting, allusively, the traditions within which a modern poet must work.’

Gergory Machecek describes two types of allusion: learned or indirect reference and phraseological adaptation, both requiring that the reader share a tradition with the author, and both sharing the element of playfulness. He writes: ‘Allusion, especially the species of allusion that I have referred to as phraseological adaptation, is a literary device involving subtle artistry and playful erudition; the impact of allusions on the meaning of a literary work can be significant and far-reaching.’ Machecek analyses the definition of allusion, and how it differs from other traditional terms, such as echo, borrowing, influence; or more recent terms, such as intertextuality. He laments the imprecise technical vocabulary surrounding the topic, and describes some of the general confusion around the boundaries between different terms: ‘For many critics intertextuality is synonymous with allusion.’ He states that certain critics ‘use intertextuality to designate what would once have been called allusions to, or echoes or adaptations of, an earlier author's work by a later writer. Their use of the term as a rough synonym for allusiveness is fairly characteristic of critical parlance.’ It seems clear that the meaning of the term intertextuality has shifted since it was originally coined by the poststructuralist Julia Kristeva in order to examine a text synchronically, and many critics feel the need for a term to describe ‘diachronic textual interrelations’.