Shakespeare's debt to his junior colleague Thomas Middleton has not yet been fully acknowledged, according to research from Birmingham University.
Not only did Middleton write significant parts of Macbeth, says John Jowett, of the University's Shakespeare Institute, but he also wrote and restructured parts of Measure for Measure.
Professor Jowett is associate general editor of a forthcoming Oxford Complete Works of Middleton - the first comprehensive study of the little-recognised 17th Century playwright for over 100 years. A great deal of new work, previously acknowledged to have been by Shakespeare, will be attributed to Middleton.
He said: "We are redefining Thomas Middleton as a major playwright. He is recognised by a few as being a major dramatist of his time, but he is not recognised enough. We are not challenging Shakespeare's general authorship, but it is clear that Middleton was significantly involved in restructuring, and sometimes additional writing."
The new findings focus on one passage of Measure for Measure. The first 80 lines of Act One, Scene Two - a dialogue between Luci and two other gentlemen - was written entirely by Middleton after Shakespeare's death, the researchers claim. "The grammar and vocabulary fit very well with Middleton," Professor Jowett said. "Each writer has certain linguistic preferences. Middleton would always write 'Oh', while Shakespeare would write 'O'. We took a very close look at the vocabulary and it was very useful."
The researchers also argue that the dialogue is filled with topical allusions to the Thirty Years War, which began in the early 1620s. Shakespeare is understood to have originally written Measure for Measure in 1603.
Professor Jowett also argues that Middleton restructured the play, adding a song to the beginning of Act Four, and switching the Duke's soliloquy to the end of Act Three. The controversial song - Take, O take those lips away - was borrowed from a play by John Fletcher, Bloody Brother, which was written in 1619 after Shakespeare died, the researchers said.