Do you put a comma in front of but

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Independent Clauses
Dependent Clauses
What About Commas After But?

This reader’s question illustrates the uncertainty felt by many writers about when to use a comma before the conjunction but:

In the following sentence, the secondary clause isn’t truly independent; it lacks a subject, yet it conveys an almost-complete thought: “I left Susan a message last week but haven’t heard back from her yet.” My question is whether a comma precedes but even though a subject doesn’t follow but. Put another way, is the secondary clause’s implied subject, I¸ sufficient to require a comma before the coordinating conjunction?

There is no “implied” subject in the sentence “I left Susan a message last week but haven’t heard back from her yet.” The sentence’s stated subject is I. It’s the subject of both verbs, the one before and the one after the but. The answer, therefore, is that no comma is needed before the but.

The rule for but is the same as that for the other six coordinating conjunctions: and, for, or, nor, so, and yet.

If the conjunction precedes an independent (main) clause, use a comma: “Jack tried a new diet, but he still gained weight.”

If the but is not followed by an independent clause, no comma is needed: “Jack tried a new diet but still gained weight.”

If a writer finds himself hesitating over a sentence like the one in the example, the easiest way to settle the comma question is to supply another subject for the second verb: “I left Susan a message last week, but I haven’t heard back from her yet.”

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Whether you should use a comma before or after but depends on the sentence construction. Recognizing the structure of a sentence will help you identify when you should use it. A few tips will make this task easy. But remember, there is always that pesky exception the rule.

Independent Clauses

Let’s begin with an example of a complete sentence.

I want the cookies.

This simple string of words contains a subject, verb and object. It is also an independent clause. It can stand on its own without adding another word. Compare that one with another one.

The store is closed.

It is also a complete sentence and an independent clause even though it doesn’t have an object as in the first example.

We can join the two clauses with a conjunction. These words function as joiners that link two sentences. They include words such as and, or and but. We can add a conjunction to our examples.

I want the cookies, but the store is closed.
He bought groceries, but he didn’t get any bread.

You’ll notice that we added a comma before but. That is because the two clauses are independent, making the comma necessary. You can test it by ending each clause with a period to see if it is a standalone sentence.

Dependent Clauses

With dependent clauses, these strings are not complete and cannot stand on their own. They include phrases missing a part of a complete sentence. We can join the two clauses with a conjunction.

I want the cookies but forgot them.
She was going to go the movie but stayed home to watch TV instead.

In this case, we didn’t add a comma because the phrase after but was a dependent clause. The bridge between the two clauses must be seamless, therefore, no comma before or after but.

What About Commas After But?

There is one situation in which you will find a comma after but. It occurs in cases where the writer makes a deliberate choice for literary effect. That’s where interrupters come into play.

An interrupter does just what the name implies. It breaks a sentence flow with a word, phrase or clause for effect. Here’s an example.

But, if you must know the truth, I never owned a lead pipe or a candlestick.

The clause, if you must know the truth, stops the flow of the sentence to interject this point. As you can see, there is a comma after but. The punctuation with an interrupter is meant to offset it from the rest of the sentence. It will always have a comma before and after its placement to draw attention to its inclusion.

Everyone was home, but, and this is important, no one heard him knocking at the door.

This goal of this sentence is to emphasize the unusual situation with an interrupter. In these cases, it’s helpful to understand the context to determine if the comma is necessary.

You should always use a comma before but when joining two independent clauses. A comma after but is only necessary if you’re using it as literary device to draw attention to something.

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