* The traditional theory: This theory holds that Shakespeare wrote all of the works attributed to him, and that any evidence to the contrary is either circumstantial or inconclusive. Proponents of this theory argue that Shakespeare was a genius who was capable of writing in a variety of styles, and that there is no need to posit multiple authors to account for the diversity of his works.
* The single-author theory: This theory holds that Shakespeare wrote all of the works attributed to him, but that he may have had help from collaborators or assistants. Proponents of this theory argue that it is possible for a single author to write a large number of works, and that there is no evidence to suggest that Shakespeare did not have help.
* The dual-author theory: This theory holds that Shakespeare wrote most of the works attributed to him, but that some of them were written by another playwright, such as Christopher Marlowe. Proponents of this theory argue that there are significant differences in style and content between some of Shakespeare's works, and that these differences can best be explained by positing multiple authors.
Theories that Shakespeare did not write all of the works
* The authorship question: This theory holds that there is significant doubt about whether Shakespeare wrote all of the works attributed to him. Proponents of this theory argue that there are a number of problems with the traditional theory, such as the lack of evidence to support Shakespeare's authorship of some of the works, and the fact that some of the works contain anachronisms or other errors that suggest they were not written by Shakespeare.
* The conspiracy theory: This theory holds that Shakespeare was a front for a group of writers who collaborated to produce the works attributed to him. Proponents of this theory argue that there is evidence to suggest that Shakespeare was not a real person, and that the works attributed to him were actually written by a group of writers, such as the Earl of Oxford or Francis Bacon.
* The ghostwriter theory: This theory holds that Shakespeare's works were actually written by someone else, such as a ghostwriter or a member of Shakespeare's company of actors. Proponents of this theory argue that there is evidence to suggest that Shakespeare was not a very well-educated man, and that he would not have been capable of writing the works attributed to him.