Modernist texts recognized more explicitly than those which preceded them that literature doesn’t exist within a vacuum. This might seem odd for a movement that rejected past ideals- even past movements in literature, like Romanticism, so blatantly. But Modernism was about reinvention as much as revolution.
TS Eliot’s The Waste Land could be considered a case study of intertextuality in Modernism because of its sheer quantity of allusions. Stylistically, this gives the poem a frenetic quality, but it also helps root some of its imagery. Take his biblical allusions, particularly evident in the descriptions of arid desert, which shows his view of a world bereft of religion.
But there’s an even greater emphasis on legendary writers such as Dante, Shakespeare, and Baudelaire. Eliot uses his references to create a coded language: in order to understand the present, he wants readers to unravel the past. It also embodies what he describes in his essay Tradition and Individual Talents as the ‘simultaneous existence’ and ‘simultaneous order’ of all texts.
For a famous example of long-form intertextuality, see James Joyce’s Ulysses. It takes its name and structure from Greek myth and Homer’s The Odyssey while also referencing The Iliad, as well as Shakespeare’s Hamlet and many others. But the novel is a culmination of many literary different styles, often depicted with an ironic gaze and using parody and pastiche.
French philosopher Roland Barthes suggests the meaning of the text doesn’t come from the text itself but from the reader’s understanding of it in relation to other texts, and this is no more evident than in Ulysses, which includes some infamously difficult passages that are hard to decode without knowledge of broad literary, historical and social influences.
It’s ironic, given that the technique has contributed to the timelessness of works.