This article in the New York Times describes the work of Dennis McCarthy who used plagiarism software to discover a source mined by Shakespeare. It seems that the Bard used a book by George North, A Brief Discourse on Rebellion and Rebels. The book had been nearly lost to history, when Mr. McCarthy came upon a clue (and you’ll have to read the article yourself to find out how this happened, or everything they discovered).
I liked this bit
One of the most compelling [evidences that Shakespeare used the book] is Jack Cade, who led a failed popular rebellion against Henry VI in 1450. Shakespeare describes Cade’s final days in “Henry VI, Part 2,” in which he says he was starving and eating grass, before he was finally caught and dragged through the street by his heels, his body left to be eaten by crows. Scholars have long thought that Shakespeare invented these details, but all of them are present in a passage from North’s “Discourse” in which he inveighs against Cade and two other famous rebels. Mr. McCarthy and Ms. Schlueter argue that Shakespeare used those details to make Cade into a composite of the three.
What I like about it is how certain scholars can be of a certain “fact” and hold this fact for many, many years — and it turns out that this fact about the most famous writer of the last 1,000 years, whose work has been ransacked for evidence of every thought was wrong. I just wonder how many facts we are certain of which are simply wrong. Our ignorance is proof of our conclusion.
The book itself looks like an interesting read (especially to see how Shakespeare reworked the source material).