Do I have to use a comma?

AnonymousHe was lying on the bed, and she was lying next to him.

The comma is optional. I would not use it in this case.

AnonymousI'd like to know if a comma is needed:

He was lying on the bed, and she was lying next to him.

When in doubt, always use the standard rule. If the next clause has its own subject, you need a comma. Your second clause has the subject "she", so the comma is required.

Here's one that must not have a comma: He was reading the

CalifJimIf the next clause has its own subject, you need a comma.

He was reading the paper and drinking coffee.There's only one clause here, right?

I get confused because no one talks about predicates anymore.

Well, I guess if we can have clauses without tenses, we can have clauses without subjects.
I know imperative sentences have been

AvangiI get confused

Join the club!

AvangiThere's only one clause here, right?

I think so.

I should not have replied to that post in the first place. My instinct is always to overpunctuate, and people keep saying that the modern approach is to use fewer commas.
The original sentence clearly has two clauses.
My question was about the teaching example, "He was reading the paper and drinking coffee."

Since I joined EF three years ago, I've seen perhaps two questions on c

Avangiif I write, "He was reading the paper, and drinking coffee" because I want a pause there, have I committed an error?

According to the English Department reader who proofread my doctoral dissertation for grammar and punctuation, yes, you have committed an error.