Personally I’ve never seen this one attributed to Shakespeare, but when the topic came up today at lunch this is the one my new boss pulled up to test me.
“The pen is mightier than the sword” actually shares a bit of infamy with “It was a dark and stormy night.” Both, you see, were by Edward Bulwer-Lytton. The latter actually inspired a contest to write in his rather unique style.
Just to regain my cred a bit (since I did not have the answer off the top of my head), I had to show my boss that Shakespeare Geek covered the topic back in April of this year, and it was reader Alexi who offered up the appropriate comment:
The one I always hear is "The pen is mightier than the sword" which is not from Shakespeare but from the 19th century novelist Edward Bulwer-Lytton, whose other contribution to literature is the phrase "It was a dark and stormy night," which is also usually attributed to someone else. In this case, Charles Schultz, creator of Peanuts.