For more than 150 years, literary sleuths have questioned whether William Shakespeare--a man with a grammar-school education, at best--could possibly have penned some of the greatest works in the English language. "You can be born with intelligence, but you can't be born with book learning," says Mark Rylance, Shakespearean actor and artistic director of the Globe Theatre in London. But if Shakespeare didn't write the plays, who did? Dozens of candidates have been proposed, most of them men. But at a conference of the Shakespearean Authorship Trust in London next week, American writer Robin Williams will argue that the true bard was a woman--Mary Sidney Herbert, the Countess of Pembroke.

Sidney (as her biographers call her) is a logical suspect. Sister of the Elizabethan poet Sir Philip Sidney, she was a poet herself and one of the best-educated woman in England, along with Elizabeth I. Perhaps not surprisingly, her name has surfaced before as a possible collaborator on Shakespeare's plays, although never until now as a candidate in her own right. Scholars are unlikely to be persuaded. "The very fact that there are so many candidates is almost a proof that none of them is the author," says Stanley Wells, chairman of the Shakespeare Birthplace Trust in Stratford-Upon-Avon. But that doesn't deter Williams. "One homicide detective told me, 'You're using the same reasoning we use to track down murderers'," she says.

In short, Mary Sidney had the motive, means and opportunity to write the plays. At her home in Wiltshire, she fostered a literary circle whose mission was to elevate English literature--a strong motive. Gary Waller, a Sidney scholar at Purchase College in New York, has called her salon "a seedbed of literary revolution" and Sidney herself "the first major female literary figure in England." With her vast library, education and command of foreign languages, Sidney also had the means to create the works. And with her extensive connections in the literary world, she had opportunity to smuggle the plays to theater companies. Perhaps it's just coincidence, but the first eight Shakespeare plays were published anonymously--"and three of them," says Williams, "provocatively note on the title page that they were produced by Pembroke's Men, the acting company that Mary Sidney and her husband sponsored."

Sidney-as-Bard would solve a number of riddles, argues Williams. It would explain why Shakespeare wrote love sonnets to a younger man. (Sidney had a younger lover, Matthew Lister.) It could clarify why the first compilation of Shakespeare's plays, the First Folio of 1623, was dedicated to the earls of Pembroke and Montgomery (her sons). And it would explain Ben Jonson's First Folio eulogy to the "sweet swan of Avon." Sidney had an estate on the River Avon--and her personal symbol was the swan. "There are swans in the lace collar and cuffs of her last portrait," Williams notes.

Even her dates dovetail with Shakespeare's--which is more than one can say of some of the other candidates. Edward de Vere, widely regarded as the leading contender, died 12 years before Shakespeare, requiring a revisionist chronology of the plays. And to embrace Christopher Marlowe, one has to believe that he faked his murder in 1593 and escaped to the European continent. "But there is growing evidence for this," says Michael Frohnsdorff, head of the Marlowe Society, add-ing that a new commemorative window in Westminster Abbey gives Marlowe's dates as "1564-1593?" Sidney's are more straightforward. She was born three years before Shakespeare and died five years after. When she suffered a series of personal losses, the plays turned darker. "It all fits," says Williams.

Case closed? Not yet. As intriguing as Williams's argument is, her evidence is circumstantial. Proof, says Sidney biographer Margaret Hannay, "would require things like letters from contemporaries praising 'Mary Sidney's Hamlet'." Until that proof turns up, scholars will stand by the man from Stratford. But that won't stop mystery lovers from trying to unseat him. The intrigue could prove as immortal as the works of the Bard--whoever he or she really was.

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