Some screenplays use the character's first names while others use the character's last names, it's just a matter of preference to the writer. I've a unique situation that has drawn a few comments... my lead character's name is Major John Mitchell and I call him Mitchell as all the character's names are their last names. A supporting character sprinkled throughout the story is Admiral Marc Mitscher and I call him Mitscher. Some comments have of course been about the similarity of the two names. I must admit it can be challenging when I read the screenplay, going from Mitchell to Mitscher back and forth. I can't change either name because it's a historical bio. Question: Is it permissible to use Admiral Mitscher or Admiral for that character? I've considered both but have noticed it is jarring and distractive when I do it.
Use Admiral Mitscher. Why tie your hands behind your back with arbitrary, self-imposed rules that make the screenplay harder to read?
If it's challenging to you, think how even more challenging it would be to your intended readers. In the great "Dr. Strangelove" script, all of the military characters have their military titles before their names. I'd probably go with all the appropriate titles for all of the military characters, too. I personally wouldn't find it more distractive, and would just kinda read through those longer character titles without any negative effect.
Bill, et. al., thanks, every character in the story and there are many, have a military rank... that makes for a lot of added words and reading, thus the reason for just using last names.... and yes, there are no rules. I think I'll use Admiral Mitscher to make him stand out from Mitchell. thanks to all,
Mike, story clarity is key. It's not "added words and reading." Yes, do be wary of the similarities between the names "Mitscher" and "Mitchell." I'd suggest going even further to distinguish one from the other and change one of the two names entirely. "Admiral" may not be enough visually on the page -- especially if the title "admiral" drops away from time to time throughout description. Consider a reader who has never seen your script before, nor knows anything about the characters. Make every effort to not cause confusion. :)
If you feel you have a problem with something in your script, you're probably right as readers will most likely notice things you hadn't considered. I, personally, would use the main character's full name and rank to make him stand out from everybody else.