To separate words or phrases of direct address from the context.
I submit, gentlemen, to your judgment.
From today, my son, your future is in your own hands.
17.

Between the name of a person and his title or degree.
Woodrow Wilson, President of the United States.
Charles W.Eliot, LL.D.
18.

Before the word _of_ connecting a proper name with residence or position.
Senator Lodge, of Massachusetts.
Elihu B.Root, Senator from New York.
19.

After the salutatory phrase at the beginning of a letter, when informal.
Dear John, When the salutation is formal a colon should be used.
My dear Mr.Smith: 20.

To separate the closing salutation of a formal letter from the rest of the sentence of which it forms a part.
Soliciting your continued patronage, I am, Very sincerely yours, John W.Smith.
21.