We know comparatively little about what Shakespeare's audience actually saw and heard, a gap in our knowledge that offers both advantages and dangers: Actors and directors need to mine the published texts for clues, but also get an enhanced permission to make free with them. The authentic tradition disappeared when England fell into civil war; attempts to recapture it amount to educated guesswork. There are very few points about which one can say with certainty how Shakespeare's company staged a given moment or what shadings they read into a particular speech. The plays' greatness makes the challenge to solve their mysteries that much more exciting. Every performance of Shakespeare is an adventure that may supply some startling revelation. The picture shows Lily Rabe and Al Pacino in this summer's New York Shakespeare Festival in Central Park production of The Merchant Of Venice.