A few months back, I asked four of my professors to write me letters for grad school. They all agreed, and to date three of those letters have been submitted. However, the last professor is still tardy on his letter, and it's already way past the due date. I'd like some advice here: Since three letters is enough for grad school, should I just say forget it and remove the last professor from all my application forms? I want to keep him on there just in case he finally decides to submit a letter in the future, but I don't know if having an unsubmitted letter affects the application. I'm having this professor for another class this semester, if that makes any difference at all.