If you have ever been uncertain regarding the capitalization of titles, the following rules may assist:
(a) Do not capitalize doctor, madam (or madame), sir, or similar names unless they occur before a proper name.
We say, “the doctor will be unable to see you”; however, “I arrived at Doctor Smith’s (or Dr. Smith’s) office at 2 pm.” “Will you be attending the play, sir?”; on the other hand, “The concert’s main attraction was Sir Elton John.” “Your taxi has arrived madame“; but “I never tire of reading Madame Bovary.” Compare: “An archbishop will preside at the conference” with “At the conference Archbishop Jones will give the keynote address.”
The same rule applies to forms of address in foreign languages: monsieur, signore, senor, effendi, and tovarich are illustrations. Note, however, there is an exception, mein Herr; Herr is always capitalized because in German, all nouns are capitalized (so I am told!).
(b) When referring to family members of a preceding generation (mother, grandfather, uncle) in direct address, capitalize. Not so for members of contemporary or succeeding generation (brother, son, cousin).
Illustrations: “When Bill’s mother and son arrived, he said, “Hop in the front of my new car, Mother; how about sitting in the back, son.’ ” At the beginning of the sentence, the speaker was addressing neither his mother or son directly, and the nouns were treated generically; but notice the different treatment in the last part of the sentence when he is addressing them directly. If you are referring causally to your mother or father, it should be my Mom and my Dad; however, referring to someone else’s parent does not get capitalized; e.g., “your mom“. If you are referring to a sibling or a child, do not capitalize: “This is my brother Bill.” “My son Charles will attend.” Again, the capitalization is reserved out of respect for the preceding generations, but not contemporary or succeeding generations.
Here, I have given you the general rule although there are those who say that none of the terms relating to kinship should be capitalized unless used directly in front of a proper name: Uncle Ed, Father John, Grandmother Sally. (See the University of Chicago Press’s A Manual of Style.) I think that is a bit harsh; if I am writing “Hi, Mom“, I think a certain degree of respect would be lost to say “Hi, mom.”
— Ken Butera