When quoting something said by someone else, should I use a comma before the quote?
Suppose I quote the definition given in a dictionary. Am I correctly using the the punctuation marks in the following sentences? (I am using them in the way I think correct in American English.)
One of the meanings of cat is, "a small animal with soft fur that people often keep as a pet."
A cadet is, "a young person who is training to become an officer in the police or armed forces."
Should I use a comma only when I explicitly quote somebody?
Groucho Marx once said, "Although it is generally known, I think it's about time to announce that I was born at a very early age."
Should I use a comma in this case too?
As Groucho Marx said,
No one is completely unhappy at the failure of his best friend.
On Comma Sense, A fun-damental guide to punctuation (Richard Lederer and John Shore), I read the following about using the comma:
Use commas to set off complete quotations:
The great general George S. Patton once said, "No, no—the war is this way, you idiots!"