When it comes to the words of great men, sometimes we discover that they did not say them or write them, but the impression continues to exist in some quarters, largely because we would rather embrace the myth than accept the reality. So it is with the following quote, attributed to Robert E. Lee:
Duty is the most sublime word in our language. Do your duty in all things. You cannot do more. You should never wish to do less.
In truth, even this rendering is an edited version of the expression upon which it is based. Those original rendering was supposedly part of a letter Lee wrote his son George Washington Custiss Lee in 1852, when the son was a cadet at the United States Military Academy at West Point. The text of the original would not appear until 1864, when it was reprinted in the New York Sun. There the phrase read like this:
Duty, then, is the sublimest word in our language. Do your duty in all things like the old Puritan. You cannot do more, you should never wish to do less.
On August 4, 1914, as the world went to war, Professor Charles A. Graves of the University of Virginia Law School addressed the issue of whether the letter was genuine. You can follow his discussion here.