A formal introduction

Do you use a comma or a colon to introduce a quote?

The Associated Press Stylebook gives us some oft-ignored pointers in the punctuation section, under "colon."

INTRODUCING QUOTATIONS: Use a comma to introduce a direct quotation of one sentence that remains within a paragraph. Use a colon to introduce long quotations within a paragraph and to end all paragraphs that introduce a paragraph of quoted material.

So ... what does that mean?

Introduce a quote with a comma if it has one sentence.

He said, "I have no idea what you're talking about."

But introduce it with a colon if it has more than one sentence.

He said: "I have no idea what you're talking about. This keeps getting crazier."

Wrong:

He said, "I have no idea what you're talking about. This keeps getting crazier."

Or, as Bill Walsh succinctly put it in "Lapsing Into a Comma": "Full-sentence quotes should be introduced with commas. Multiple-sentence quotes should be introduced with colons."

And an exception: Some newspapers will have you use a colon with one sentence if you're flipping the attribution ("Said he:" vs. "He said,").