More billions of words of analysis and conjecture have been written on Shakespeare than on any other artist, not merely of the millennium but in the history of the planet.

Yet no scholar or would-be biographer would claim to have got closer to explaining his genius than did Arthur Mee, a now despised Edwardian populariser. Mee simply said in his Children's Encyclopaedia (1908): "He was a giant who once walked on this earth."

Yesterday the critic John Casey, Fellow of Caius College, Cambridge, was no less baffled than his predecessors. Reacting to the Today programme poll, Dr Casey said Shakespeare's 154 sonnets were the greatest love poetry in literature. "Yet they reveal nothing. We know almost nothing about him."

In his play Antony and Cleopatra, he had given Cleopatra a line with an exquisite sense of power and sexual attractiveness:

... his delights
Were dolphin-like, they show'd his back above
The element they liv'd in ...
Yet the man who wrote this, Dr Casey said, had probably never seen a dolphin.

His fellow Elizabethan playwright Ben Jonson, who did know him, was vindicated in prophesying he was "not for an age but for all time". But by the Victorian period, a strong puzzlement had crept into the tributes.

This is because we know virtually nothing about Shakespeare's life. He was born in 1564 and died in 1616. We know that as a poet he moved from the florid, Italian-influenced verse of his early plays to a final starkness in King Lear which anticipates and far outstrips the starkness of Samuel Beckett. But we do not reliably know what he or even his handwriting looked like. His gravestone at Stratford-upon-Avon, where his tradesman father sent him to grammar school, is nameless.

We can establish that after he made his first impact on literary London in 1592, the million or so words that he wrote earned him enough to buy New House, a large Stratford house. But we know little about how his professional life moulded the artistry which made this money.

Scholars still quarrel without hope of finding proof of the identity of the Dark Lady of his sonnets, of his feelings about the death of his son Hamnet, or of his true relations with his wife, Anne Hathaway.The few bones on his biographical skeleton come from registers of birth, marriage, death and burial, conveyances and other legal documents. At best these are "dusty details", one scholar says.

Matthew Arnold summed up the mystery in 1849:

Others abide our question. Thou art free,
We ask and ask: Thou smilest and art still,
Out-topping knowledge.