In 1995 Unesco named April 23 World Book Day because of a morbid literary coincidence. Both William Shakespeare and Miguel de Cervantes died April 23, 1616, the same exact date but 10 days apart, since England was on the Julian Calendar while Spain was on the Gregorian. It's a fortunate coincidence (or near coincidence) because collectively, they produced one of the greatest missing literary works of all time, the play "Cardenio." And on World Book Day I always find myself thinking about the books that don't exist more than the ones that do.

We know almost nothing about "Cardenio." The King's Men, that uniquely blessed theater company that held the privilege of staging new Shakespeare material, performed the play before James I in May and June of 1613, and no contemporary record other than the fact of the performances has survived. Shakespeare most likely co-wrote the piece with his favorite collaborator, John Fletcher, who often used Spanish novels as a source for his drama. We assume the play was based on Cervantes' novel "Don Quixote" because Cardenio is the name of a major character from the book, and the material was timely; Thomas Shelton released his celebrated translation of the "Quixote" in 1612.

While it may seem inconceivable to us that the smallest scraps of Shakespeare's genius would fail to be preserved like holy relics, oblivion was not an uncommon ending for plays of the early 17th century. Shakespeare's "Pericles" exists only in a lousy quarto, which is so badly transcribed scholars assume it was done by someone jotting down the script from memory after having seen the show (the early modern equivalent of the grainy pirated videos you can buy on the subway). Like most dramatists of the period, Shakespeare didn't care about his plays after their performances, made no effort to publish them and received no money from their publication.