FROM GILFINDEL
So help me out here. Where are commas needed, tolerated, or banned, particularly in compound sentences (another thing I'm apparently fond of, along with parenthetical statements)? In particular, would you use a comma before the "and" in any of the following sentence patterns:
1) This happened and that related thing happened.
2) This happened and that unrelated thing happened
3) This happened and then that happened.
4) That and that happened and then that other thing happened.
5) This and that happened.
My general habit is "no" for 1, 2 and 5 and "yes" for 3 and 4, largely to indicate a brief pause in the sequence of events, but is that actually correct?
As a follow-up, what if "and" is replaced with "but"? Does that change anything? I suspect the answer should be "no", but that just looks strange to me (as you can tell by the comma I just inserted in this statement).
RESPONSE
If there's a subject and a predicate (a complete sentence) before and after "and" use a comma before "and". Same for "or". If "and" or "or" connects two nouns to one verb or two verbs to one noun, no comma.
1) This happened, and that related thing happened. (a subject and predicate before and after "and")
2) This happened, and that unrelated thing happened. (a subject and predicate before and after "and")
3) This happened, and then that happened. (a subject and predicate before and after "and")
4) That and that happened, and then that other thing happened. (first "and" connects two nouns to one verb, second "and" has a subject and predicate before and after it)
5) This and that happened. ("and" connects two nouns to one verb)
6) This happened and astonished everyone. ("and" connects two verbs to one noun)
In a list of three or more things, always use a comma before "and" or "or". The exception is pairs considered as a single unit, then no comma. So:
I like baseball, hotdogs, and apple pie.
I like Cher, Bono, and Donnie and Marie.
That's about it for "and" and "or" off the top of my head.
I typically use a comma before "but" because 99% of the time, "but" indicates an exception to whatever came before it and usually has a subject and predicate before and after it. However, when "but" connects two adjectives like "short but sweet", no comma. Also, don't use a comma when "but" is used in what I call negative exclusions and inclusions:
Nobody but Allen danced with Nancy. (excludes "Allen" from "Nobody")
The phantom not only killed but mutilated his victims. (includes "mutilated" with "killed")
And of course, there are colloquialisms that use no comma like "anything but that" and "all but <adjective>, but for standard everyday usage in your average compound sentence, "but" usually likes a comma.
You know, all those conjunctions really function the same way. Essentially, if you use them to connect two sentences, use a comma, if you connect anything else, don't. How's that for short and simple? Of course, this is English, and there are about a bajillion exceptions, but if you start there, you'll be OK the majority of the time.