Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
Sir, Dame
The British title for knight or baronet can be a trap for unwary Americans: it can’t be used with just the last name. The English actor is Sir John Gielgud, or Sir John, but never Sir Gielgud. The same rule applies to Sir’s female counterpart, Dame (which see): it’s Dame Agatha Christie, or Dame Agatha, but never Dame Christie.
Uncapitalized, sir is the term used in direct address to a man whose name is unknown or to whom you intend to show respect: Thank you, sir. Ma’am and madam are the terms used for these purposes for women.
