Reblogged from Just Can’t Help Writing:

Commas are among my favorite tools for building meaning. Used intelligently, commas are wonderful signposts that tell readers which part of a sentence they’ve stumbled into—and then help them make their way out again. I like commas so much I’ve written multiple posts about them.

If comma rules confuse you, take heart! If improving reader comprehension is your goal, there are really only a few “rules” to remember:

Use commas:

Rule 1: After introductory elements.

This is the one most people seem to know about. But I argue that commas are really only necessary when the introductory element gets long enough that readers may miss the lane change back into the main part of the sentence.

So:

After a moment he left the room. (No comma needed unless you want to emphasize a pause.)

But:

After he spent  an extended vacation in a remote village in the Alps, where did he go next? (The comma lets readers know that “where” begins a new clause.)

Rule 2: Around or after “interrupters,” including non-essential modifiers (this is a rule, not an option).

I think this one is the most confusing for many writers.

Short interrupters can be easy to spot:

Jane, however, did not go with him to the Alps.

However, Jane did not go.

Non-essential modifiers are elements that can be lifted out of the sentence without compromising its meaning or purpose.

The old car, which was a lot like the one my grandfather used to drive, had been repainted bright blue.

The information about grandad’s car is incidental to the meaning of the sentence, which is that the car is now bright blue. Lift it out and only this incidental information is lost. The rule here, and it IS a rule, is TWO COMMAS, not just the first one. You need that second comma to signal the return to the main clause.