The question of how many plays William Shakespeare wrote is one of some dispute among scholars. There are of course the various factions that believe he did not write any of the works attributed to him. And there's the question of whether he co-wrote a play titled "Double Falsehood", which was previously attributed to Lewis Theobald.
The majority of Shakespearean scholars agree that he wrote 38 plays: 12 histories, 14 comedies, and 12 tragedies. But several theories persist that question that total.
Shakespeare and 'Double Falsehood'
After many years of research, Arden Shakespeare published “Double Falsehood” under the name William Shakespeare in 2010. Theobald long claimed his work was based on a lost Shakespeare work, whose title was believed to be “Cardenio,” which was itself based on a section of Miguel de Cervantes “Don Quixote.”
It's still not fully incorporated into the canon, but may be over time. “Double Falsehood” is still debated by scholars; many of whom believe it bears more of the hallmarks of its co-author, John Fletcher, than of William Shakespeare. It's hard to say when, or if, it will be universally recognized among Shakespeare's other plays.
Christopher Marlowe and Other Would-Be Shakespeares
Then, there are the numerous theories which rest on the assumption that Shakespeare, for whatever reason, could not or did not write all (or any) of the plays that bear his name.
Some Shakespeare conspiracy theorists believe he was not well-educated enough to have written so eloquently and so prolifically. Other theories suggest that the name William Shakespeare was a pseudonym for an author or authors who wished to remain anonymous for some reason.
The leading contender for the role of the “real” Shakespeare is playwright and poet Christopher Marlowe, a contemporary of the Bard. The two men were not exactly friends but did know each other.
The Marlovians, as this faction is known, believe Marlowe's death in 1593 was faked, and that he wrote or co-wrote all of Shakespeare's plays. They point to similarities in the two authors' writing styles (which can also be explained as Marlowe's influence on Shakespeare).
In 2016, the Oxford University Press even went so far as to credit Marlowe as a co-author of its publications of Shakespeare's "Henry VI" plays (Parts I, II and III).
Edward de Vere and the Rest
The other leading candidates for the “real” Shakespeare are Edward de Vere, 17th Earl of Oxford, a patron of the arts and noted playwright (none of his plays survive, apparently); Sir Francis Bacon, philosopher, and father of empiricism and the scientific method; and William Stanley, 6th Earl of Derby, who signed his works “WS” just like Shakespeare did.
There's even a theory that some of all of these men collaborated to write the plays attributed to Shakespeare, as one elaborate group effort.
It's worth noting, however, that any “evidence” that anyone other than William Shakespeare wrote his 38 (or 39) plays is entirely circumstantial. It's fun to speculate, but most of these theories are considered little more than fringe conspiracy ideas by the most knowledgeable historians and scholars.
The full list of Shakespeare plays brings together all 38 plays in the order in which they were first performed.