Usually, the only time you should use a comma after “but” is when “but” is followed by a parenthetical element. Use a comma before “but” if it’s at the beginning of an independent clause.
Playing fast and loose with your commas is rarely a good idea, but it’s something that happens regularly. There are quite a few rules in the English language governing the use of commas, so instead of learning all of them some writers let their natural sense of rhythm guide their comma usage. That’s why you’ll often hear that commas should be used where you’d pause if you were speaking. Sometimes there is indeed a correlation between pauses in speech and proper comma placement. But learning the rules of comma usage takes the guesswork out of writing and cuts down your chances of making a mistake. Here we’ll demonstrate how a couple of these rules apply to the word but.
What’s But About?
We often come across the word but when it plays the role of a conjunction, a word that connects words, clauses, and parts of sentences. Here’s an example of the word but being a very useful little conjunction:
We wanted to go on vacation this summer, but we couldn’t get the time off work.
As a conjunction, but is commonly used to introduce a clause or phrase that contrasts with the one preceding it:
I wanted to say something, but I decided to stay quiet.
But can also be used as preposition, and in that case it means “except” or “apart from”:
The fire spread to all but the lowest floors.
There’s also the adverbial use of the word but, in which case it means “only”:
He was but a fishmonger’s son.
But, Commas, Conjunctions
If we want to learn a rule or two about using commas in sentences, and we’d like to use the word but to help us out, we’d have to use it as a conjunction. Let’s take a look at two sentences where but is a conjunction:
Her hair wasn’t black but dark brown.
Spots was a happy cat, but he still tried to get outside every chance he got.
As you can see, the first sentence contains no commas, while the second sentence has a comma before but. In the first sentence, but is used to connect “dark brown” with “her hair wasn’t black.” If you think about it, you’ll see that “dark brown” is not an independent clause. It can’t stand alone without “her hair wasn’t black.”
In the second sentence, however, each of the two clauses that form it can stand as independent sentences—that makes them independent clauses. You can say “Spots was a happy cat.” And then you could say “he still tried to get outside every chance he got.” And that brings us to the comma usage rule:
Use a comma before a conjunction only when the conjunction is at the beginning of an independent clause.
Now let’s see if there’s a situation where a comma can be used after but. Let’s check in with Spots again:
But, of course, it’s not safe for Spots to go outside on his own.
Yes, the sentence above is correct. So it is possible to use a comma after but. There are two things going on in this sentence—but is used at the beginning, and but is immediately followed by an interrupter phrase. The fact that we’ve started the sentences with a conjunction has no effect on the comma usage, but the interrupter phrase does:
Interrupters, or parenthetical expressions, are phrases or clauses that are inserted into a sentence and that could be removed without changing the meaning of the sentence. They are always separated from the rest of the sentence by commas or parentheses.
That’s another comma rule—you should use commas to set off interrupters. If they happen to appear after a conjunction, you have a situation where it’s okay to use a comma after but.
Posted: July 18, 2016 on Grammarly.com Blog