On this day in 1616, April 23, William Shakespeare died, and Miguel Cervantes was buried. Three hundred and ninety-nine years later, the play connecting them still confounds us. Of course, Shakespeare was also born on this same date 451 years ago.

A play is lost

Three years before, in 1613, royal records give evidence of the performance of a play called Cardeno by The King's Men, the famous acting company that Shakespeare was associated with, for which they were paid. At the time Shakespeare was collaborating with another writer named John Fletcher – they wrote Henry VIII and The Two Noble Kinsmen together – for the King's Men. Forty years later, in 1653, leading publisher Humphrey Moseley asserted his right to publish the play, but ultimately never did. The play was lost, and would go on to be one of the most hotly contested lost plays attributed to the Bard.  Only two things are known: one, that it is based on episodes from Don Quixote, and two, that Fletcher and Shakespeare co-wrote the play.

What happened next

More than a hundred years later, things took an interesting tun. A well-known Shakespeare editor and a (minor) playwright, Lewis Theobald, produced a play in 1727 called Double Falsehood, or The Distrest Lovers, which he claimed was adapted from Cardenio, based on a manuscript that Theobald had discovered. His great rival and archenemy, Alexander Pope, vociferously opposed this claim. Pope disliked Theobald immensely, especially after Theobald had pointed out several inaccuracies in the former's editions of Shakespeare's works. Pope's campaign to discredit Theobald's claim was successful.

But although this charge of fraud stuck for over 175 years, recently literary scholars have been reading and re-reading the play and finding the touch of Shakespeare lurking in Double Falsehood, especially in the repartees and the long passages of this play.

What the software revealed

One such scholar is Robert Flockenflick, a Professor Emeritus at UC-Irvine. He recently invited two researchers at the University of Texas, Ryan Boyd and James Pennebaker, to investigate this mystery, using a computer programme to measure the "categorical dynamic index" of the three writers – Shakespeare, Fletcher and Theobald – and try to trace them by evaluating how they used simple words, especially pronouns. In effect, Boyd and Pennebaker said, they were looking for the "psychological imprint" of Shakespeare through mining the text using their computer-based analysis.

The programme uses a scale with the "dynamic" at one end and the "categorical" at the other to examine the words used by a writer. While people who're natural storytellers and are generally outgoing fall near the former end, those with a more reticent and conservative nature tend to fall nearer the latter. What they found was that John Fletcher's words fell near the dynamic end of the spectrum, while Theobald's fell close to the categorical end. Somewhere in the middle lay Shakespeare's words. The researchers claim that this proves that Shakespeare's own writing exists within Theobald's adaptation.

This result was announced at a UCLA conference recently, and met with approval among scholars of Shakespeare who were present. Whether this truly is a scientifically valid way of determining Shakespeare's authorship or not – or whether such a thing is even possible to compute using the methodology of the natural sciences – Double Falsehood is fast shaping up to have the most believable claim of originality in all his other Shakespeare's 'lost' works.

The Renaissance scholar and editor of the New Oxford Shakespeare, Gary Taylorbelieves that Theobald's play is indeed based on a manuscript of Cardenio written by Shakespeare and Fletcher. For him, the greater problem lies with the fact that he considers Theobald a not very good playwright. After years of painstaking recasting of Double Falsehood, where he attempted to lose the bits in the play that was clearly from the 18th century, he staged The History of Cardenio (he believes that is what the play would have been called in 1613) in 2012.

There have been other attempts to resurrect this lost play, notably by the Arden Shakespeare edition of Double Falsehood and a recent Royal Shakespeare Company staging. But not everyone is convinced by the various claims made about the play. Considering that there are as many conspiracy theories about Shakespeare as there are college papers about his works, one thing is clear - this won't be the last we'll hear about Cardenio.