Ah, the comma. Arch-nemesis of writers. I think I know all the rules on commas until I start writing. Then I start throwing commas around like confetti, and half of them don’t land where they belong. I’m getting better at it, but there are specific instances I always have to stop and look up.

I’m not going to bother writing this post about setting off appositives or whether or not to use a serial (oxford) comma for lists (you should!!). I’m just going to focus on my buggaboo – the comma preceding a conjunction.

Conjunctions followed by Sentence Fragments

So the easy one that I never have problems with is when the conjunction is NOT followed by a subject + verb.

For instance — no comma:
The Doctor invited Rose into the TARDIS and showed her the universe.

As opposed to — comma:
The Doctor invited Donna into the TARDIS, and Donna showed him her sassy attitude.

I know this rule cold, and yet I make this mistake ALL the time drafting. I have to keep an eye out for it.

Conjunctions followed by subject + verb

I run into problems when I encounter conjunctions followed by a subject because some do and some don’t require a comma, and it all has to do with whether the conjunction is coordinating or subordinating. But I prefer memorizing a list because I have no earthly clue when a sentence is being subordinated or coordinated or subdued or cooperative or whatever.

So here we go. My cheat sheet. You can point and laugh at me, but when I get stuck in the future, I’ll have this list to double check.

Coordinating conjunctions

Coordinating conjunctions tie together two INDEPENDENT clauses. I read this as sentences you could conceivably say without the other part. I’m kidding. I just memorize this list:

and

but

or

not

yet

for

nor

so

Examples:
We’re celebrating Darcy’s birthday, for he’s more or less a jolly good fellow.
I swear I’ll stop swearing in blog posts, yet I’m only human.
You thought I was going to swear just then, but I didn’t.

One caveat:
It’s possible for an “and” or “but” to be part of a dependent clause. If you start with one a subordinating conjunction (see below) and there are two dependent clauses attached to the conjunction, you do not need a comma. This is tricky, so you have to read the sentence and evaluate it.

Example:
You have to proofread constantly if commas dog you and you want to root them out.

In the above, both “commas dog you” and “you want to root them out” are dependent on “if,” so you don’t need a comma. Proofread carefully.

Subordinating conjunctions

Subordinating conjunctions tie together an INDEPENDENT clause with a DEPENDENT CLAUSE.

For instance in the following sentence:
I would go climb aboard the TARDIS in a heartbeat if the Doctor invited me.

You have an independent clause: I would go climb aboard the TARDIS.
And a dependent clause: If the Doctor invited me.

They tell me the dependent clause cannot stand alone, but I figured it was just drunk. Now you can start or finish a sentence with the dependent clause, and the comma rules on that are as follows:

If you start with the dependent clause, you need the comma:
If the Doctor invited me, I would climb aboard the TARDIS.

But if you follow with it, then there’s no comma:
I would climb aboard the TARDIS if the Doctor invited me.

Here’s a list of subordinating conjunctions:

after	although	as	because	before	even if
even though	if	in order that	once	provided that	rather than
since	so that	than	that	though	unless
until	when	whenever	where	whereas	wherever
whether	while	why

A couple of caveats.

1. Note that “so that” is a subordinating conjunction and “so” is a coordinating conjunction. This becomes tricky when you drop the “that” from “so that.” I literally read every “so” in my MS followed by a mental “that” to figure out which of these I’m using. If you can put in the “that,” then you don’t need a comma. Alternately, you can often stick “and” in front of the “so” that needs the comma.

Examples:
I am writing this blog post so (that) I have this list within easy reach.
I am writing this blog post, (and) so I should no longer have an excuse to make mistakes.

2. While is another tricksy one. While can mean “at the same time as” or it can mean “whereas”. Now, as you can see in the above list “whereas” is a subordinating conjunction, so you’d tend to think that you wouldn’t need a comma before while, however, there’s this one weird nitpicky rule: If you use “while” to mean “whereas,” you must set it off by a comma.

Examples:
My friends are writing while I’m obsessing over commas. (At the same time)
Some comma rules are easy, while this one is a pain in the ass. (whereas)

If you can think of any other weird exceptions or just want to argue with my admittedly flimsy grasp on the whole issue, please feel free to leave a comment.

GOOD LUCK!