I always thought Black Tie on an invitation means you must wear a tuxedo (men). Who agrees?
My mom and sister think a dark suit is acceptable. My cousin (who is mother of the groom) says plenty of men will be in suits. So I told DH this and he said he does not want to be the only one not in a tux. Not that he's crazy about renting when he has a gorgeous suit to wear.
My sister who used to work on high-end invitation says you shouldn't even put Black Tie on an invite, it's implied based on the wedding day/time and location.
Tux if it just says Black Tie. Most hosts are putting black tie optional to let their guests know that black tie is not required. Once upon a time, everyone knew that an evening wedding was black tie but this is no longer the case.
To me Black Tie means tux. I always thought the whole point of Black Tie optional meant that people could wear a suit in that instance. I know any weddings we've gone to that have just said Black Tie DH has always worn his tux.