shakespeare's main source is believed to be an earlier play—now lost—known today as the "ur-hamlet". possibly written by thomas kyd, the "ur-hamlet" would have been in performance by 1589, and was seemingly the first to include a ghost in the story. shakespeare's company, the chamberlain's men, may have purchased that play and performed a version, which shakespeare reworked, for some time. since no copy of the "ur-hamlet" has survived, it is impossible to compare its language and style with the known works of any candidate for its authorship. consequently, there is no direct evidence that kyd wrote it, nor any evidence that the play was not an early version of "hamlet" by shakespeare himself. this latter idea—placing "hamlet" far earlier than the generally accepted date, with a much longer period of development—has attracted some support, though others dismiss it as speculation. francis meres's "palladis tamia" (published in 1598, probably october) provides a list of twelve named shakespeare plays, but "hamlet" is not among them. this is not conclusive, however, as other then-extant shakespeare plays were not on meres' list either.