Q. I cannot find anything in CMOS to corroborate my hunch that a capital should be used in cases like the following: (1) “Please note: It is important to unplug the appliance after using it.” (2) “Hint: You may not need all the letters to solve the puzzle.” (3) In the acknowledgments section of a book, “Jennifer, James, and Joe: Thank you for all your support.” Some might argue that the word following the colon in each of those instances should begin lowercase, as in the second example under paragraph 6.61, but that doesn’t seem right to me. Thanks for your help.
A. We agree with your hunch. When a word, a phrase, or a dependent clause introduces a complete sentence with the help of a colon, that sentence usually gets a capital letter:
Note: Semicolons are not allowed past this point.
and
Please note: Semicolons are not allowed past this point.
This is exactly how speech tags work (and see CMOS 6.65):
She said, “Find your own way.”
or
She said: “Find your own way.”
Some style guides advise capitalizing the first word of any full sentence that follows a colon, but Chicago’s more traditional approach treats a colon between two complete sentences as it would a semicolon:
Semicolon
The party lasted until exactly midnight; that’s when the gas in the generator ran out.
Colon
The end of the party was signaled by an abrupt silence: the generator had run out of gas.
If the lowercase letter after the colon in that last example is too subtle for your purposes, you have our permission to depart from Chicago and apply a capital letter—or maybe try a dash instead.