What the analysis found

Computerised textual analysis has pushed the case for Shakespeare's authorship of Edward III beyond any reasonable doubt, according to researchers who say the Stratford-born playwright was the principal writer of the play. Dr Rory Loughnane, a reader in early modern studies at the University of Kent and general editor of the Oxford Marlowe editorial project, worked on the study with Brett Greatley-Hirsch, a professor of renaissance literature and textual studies at the University of Leeds.

The researchers put the play side by side with securely attributed works by 10 dramatists active between the late 1580s and the mid-1590s, running several kinds of computerised linguistic analysis. Instead of pinning individual lines on a writer, they tracked linguistic features and how certain "marker" words were spread through the text - words such as "martial", which turn up often in Marlowe's plays but rarely in those of his contemporaries.

One test of the play's segments came out decisively in Shakespeare's favour: 23 segments - "the lion's share" - were assigned to him, and nine were assigned to Marlowe, the writer behind Doctor Faustus.

A newly found collaboration

The research, co-authored by Loughnane, concludes that Edward III should be added to William Shakespeare's canon and that it was a major collaboration with his contemporary rival Christopher Marlowe.

"That's the new finding, that both Shakespeare, now confirmed beyond doubt, and Marlowe, unexpectedly found for the first time, are present in the play," Loughnane said.

"Our new research suggests that Marlowe is Shakespeare's collaborator on Edward III. This is the first time this case has been made seriously," he said.

In his view, the discovery has massive implications for understanding the relationship between the two most important dramatists of the period, and it changes both the Shakespeare and the Marlowe canons. He pointed out that Marlowe and Shakespeare are usually treated as rivals - two outstanding authors, born within weeks of each other, working in the same theatrical world of the late 1580s and early 1590s - but that their relationship was much more complicated. "They were not simply rivals or influences on one another," he said.

The collaboration on Edward III dates to 1592, which Loughnane said suggests a more sustained writing relationship in their mid-to-late 20s. Marlowe died aged just 29, after a brawl in a lodging house in 1593.

From anonymous 1596 play to the canon

The history play was published anonymously in 1596, though it has long been thought that Shakespeare wrote at least a few scenes. It did not appear in the 1623 first folio collection of Shakespeare's plays.

Earlier editions had already given Shakespeare partial credit: the play appeared in a 2005 volume, and Loughnane edited it for the 2016 New Oxford Shakespeare: Complete Works, acknowledging that a couple of scenes had probably been written by Shakespeare. He also co-authored the Canon and Chronology study in the New Oxford Shakespeare: Authorship Companion, which made the case for Shakespeare's part-authorship while noting that further research was needed.

Example speeches and publication

The analysis confirms a speech from the beginning of scene 13 as Shakespeare's, written at a moment when a sudden and ominous darkening of the sky causes fear in the French camp, and King Jean says "A sudden darkness hath defaced the sky …". A speech from the final scene was classified as Marlowe's: "Great servitor to bloody Mars in arms, / The Frenchman's terror and his country's fame".

A 2016 study had already found that Marlowe was a co-author of Shakespeare's three Henry VI plays. The new research will be published in Shakespeare Quarterly later this year. Loughnane's book Shakespeare at Thirty, exploring Shakespeare's early career, is published by Princeton University Press this week, and his exhibition The Making of Marlowe runs until 22 November at the Beaney House of Art & Knowledge in Canterbury.