Why do English teachers hate this? I always figured that was the whole point of a comma.
Well, it’s pretty unreliable. Different readers put pauses in different places, many of which are not indicated by a comma. A comma usually does indicate some sort of pause when reading out loud, but a pause doesn’t always indicate a comma. For example, for me, when reading aloud, I can’t tell the difference between:
“I got in the car and drove down to the park to pick up Billy.”
and
“I got in the car, and I drove down to the park to pick up Billy.”
If I wrote it as I say it, it would either come out as “I got in the car, and drove down to the park to pick up Billy” (which has a comma splice) or “I got in the car and I drove down to the park to pick up Billy” (which should have a comma because of the two independent clauses.) I may read it with a slight hesitation between the two clauses, or I might not, but most manuals of style will tell you that the first sentence should not have a comma, and the second requires it. So using your ear is not necessarily a reliable way of determining which one is correct.
Neither is a style guide. A style guide is a matter of opinion that is used by some given group to lend consistency to the writing, rather than a matter of right and wrong.
The grammar books and English teachers will say the same thing, too (about the comma examples I’ve given), but I’m trying not to get into the “what is correct grammar” discussion. At any rate, the two particular rules I’ve given on comma usage are the rules for standard written English, so much as standard written English can have an agreed-up set of rules.
Only if you put a comma after them.