Put a comma before “but” when it connects two independent clauses—two groups of words that could each stand alone as a complete sentence. Put a comma after “but” only when an interrupter (a word or phrase like “of course” or “unsurprisingly”) follows it directly. In all other cases, no comma is needed with “but.”
“But” is one of the most common words in the English language—and one of the most misused when it comes to comma placement. Writers either drop commas before it out of habit or add them everywhere, treating “but” like a universal comma trigger. Neither approach is correct.
The rules governing comma placement with “but” are actually consistent and logical once you understand what “but” is doing in a given sentence. This post covers every major scenario: comma before “but,” comma after “but,” no comma at all, and the special cases that trip up even experienced writers. By the end, you will have a clear, repeatable method for getting it right every time.
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What Kind of Word Is “But”?
Before addressing comma placement, it helps to understand what “but” is grammatically. “But” is a coordinating conjunction—one of seven listed under the acronym FANBOYS: For, And, Nor, But, Or, Yet, So.
Coordinating conjunctions connect two grammatically equal elements. Those elements can be single words, phrases, or full clauses. The type of element “but” is connecting determines whether a comma belongs before it.
The same rule that applies to “but” applies to all FANBOYS conjunctions. Understanding the logic for “but” means you understand it for “and,” “or,” “so,” and the rest.
When Should You Put a Comma Before “But”?
The rule is precise: use a comma before “but” when it joins two independent clauses.
An independent clause is a group of words that contains both a subject and a verb and can function as a complete sentence on its own.
Consider this example:
I would go for a walk, but it’s raining outside.
The clause before “but”—I would go for a walk—is a complete sentence. The clause after “but”—it’s raining outside—is also a complete sentence. Both are independent. A comma before “but” is required.
According to the Purdue Online Writing Lab (OWL), one of the most widely cited grammar authorities in academic writing, commas should separate independent clauses joined by any of the seven coordinating conjunctions. This is a foundational rule of English punctuation, not a stylistic preference.
More examples with two independent clauses:
The lights are on, but no one is home.Clint looked at me, but he didn’t speak.They spent hours on the fishing boat, but they didn’t catch anything.It’s sunny, but it’s cold outside.
In each case, both sides of “but” could stand alone as separate sentences. A comma is required before “but” in all of them.
How Do You Test Whether a Clause Is Independent?
The test is straightforward. Cover “but” and the words after it, then ask: does what remains form a complete sentence?
Then cover “but” and the words before it, and ask the same question about what follows.
If both pass the test—if both halves are complete sentences—use a comma before “but.”
If either half fails—if one side lacks a subject, a verb, or the ability to stand alone—no comma is needed.
When Do You NOT Need a Comma Before “But”?
This is where many writers overcorrect. Not every use of “but” requires a comma. When “but” connects an independent clause to a dependent clause or a sentence fragment, the comma is dropped.
A sentence fragment is a clause missing a subject, a verb, or a complete thought. It cannot stand alone.
Compare these two sentences:
I would go for a walk, but it’s raining outside. ✅ (comma required—two independent clauses)I would go for a walk but for the rain. ✅ (no comma—”for the rain” is a fragment)
The phrase for the rain has no subject and no verb. It cannot be a sentence. Because the second element is not independent, no comma precedes “but.”
Scribbr’s grammar reference identifies this as one of the most common comma errors writers make—adding a comma before “but” when the second part is a fragment, not a full clause.
More correct examples with no comma needed:
Tom likes cake but not pie. (fragment: “not pie” has no subject or verb)It’s sunny but not warm outside. (fragment: “not warm outside” lacks a subject)The dog is young but well trained. (fragment: “well trained” cannot stand alone)Grammar is boring but necessary. (fragment: “necessary” is a single word)
How Can You Simplify Long Sentences to Avoid the Comma?
When a sentence uses two independent clauses with the same subject, you can often remove the second subject and merge the predicates. This eliminates the need for a comma entirely.
Clint looked at me, but he didn’t speak. → Clint looked at me but didn’t speak.They spent hours on the fishing boat, but they didn’t catch anything. → They spent hours on the fishing boat but didn’t catch anything.
Both revised versions are correct. The second clause no longer has its own subject, so it is no longer independent, and the comma is dropped. This technique is particularly useful when shortening content without sacrificing clarity.
When Do You Put a Comma After “But”?
A comma after “but” is needed in only one situation: when “but” is immediately followed by an interrupter.
An interrupter is a word or phrase inserted into a sentence to convey emphasis, tone, or mood. It is not grammatically essential—you can remove it without changing the meaning of the sentence. Common interrupters include of course, unsurprisingly, to be fair, as you can see, and needless to say.
Because interrupters are parenthetical, they are enclosed in commas on both sides.
When one appears directly after “but,” the structure looks like this:
But, of course, it’s not safe for Spot to go outside on his own.Karen nodded, but, unsurprisingly, she wasn’t paying attention.The course is interesting but, for all intents and purposes, merely introductory.
Remove the interrupters and the sentences still make complete sense: Karen nodded, but she wasn’t paying attention. The interrupter adds texture but not meaning.
Outside of this specific scenario, a comma after “but” is almost always an error.
Does Starting a Sentence with “But” Require a Comma After It?
No. Despite longstanding classroom myths, beginning a sentence with “but” is grammatically acceptable. More importantly, it does not automatically require a comma after “but.”
But he doesn’t know where he wants to go. ✅ (no comma after “but”)But, of course, he doesn’t know where he wants to go. ✅ (comma after “but” because an interrupter follows)
The comma is triggered by the interrupter, not by the position of “but” at the start of the sentence.
What About “Not Only…But Also”?
The correlative conjunction pair “not only…but also” follows a slightly different rule. According to Grammarly’s style guidance, a comma is generally not used with this construction unless the two clauses it connects are both fully independent.
The market is open not only on Saturday but also on Sunday. ✅ (no comma—not two independent clauses)She not only completed the project, but she also presented it to the board. ✅ (comma—both clauses are independent)
The same independent clause test applies here. When both halves of a “not only…but also” sentence could stand alone as complete sentences, a comma before “but also” is appropriate. When they cannot, leave the comma out.
Common Mistakes Writers Make with Comma Placement and “But”
Understanding the rules is useful. Recognizing where errors typically occur is equally important.
Mistake 1: Adding a comma before every “but”
Many writers treat “but” as a universal comma trigger. It is not. Comma before “but” applies only when both connected clauses are independent. “She tried but failed” needs no comma. “She tried, but she failed” does.
Mistake 2: Omitting the comma when two independent clauses are present
The reverse error is also common—skipping the comma when “but” connects two clauses that could each be complete sentences. “I wanted to stay but I had to leave” is missing a comma. The correct version is “I wanted to stay, but I had to leave.”
Mistake 3: Placing a comma after “but” without an interrupter
A comma after “but” is almost never correct unless an interrupter immediately follows. “But, I don’t agree” is incorrect. “But I don’t agree” is correct. The comma serves no function there and introduces an unnecessary pause.
Mistake 4: Misidentifying fragments as independent clauses
The most reliable fix for this error is applying the independent clause test consistently. If the words after “but” cannot stand alone as a sentence, no comma belongs before “but.”
A Quick Reference: Comma Before or After “But”
| Situation | Comma? | Example |
| “But” connects two independent clauses | Before “but” | She studied, but she didn’t pass. |
| “But” connects a clause and a fragment | No comma | She studied but didn’t pass. |
| “But” followed by an interrupter | After “but” | But, of course, she studied. |
| “But” connects two independent clauses + interrupter | Before and after “but” | She studied, but, unsurprisingly, she didn’t pass. |
| “But” starts a sentence (no interrupter) | No comma | But she didn’t pass. |
Mastering Comma Rules Builds Better Writing
Comma placement is one of the more reliable indicators of writing quality. Getting it right with “but” requires only one consistent habit: check whether both clauses are independent before adding a comma, and check whether an interrupter follows “but” before adding a comma after it.
These two tests cover the vast majority of real-world situations. The independent clause test is the more important of the two—apply it first, and comma errors with “but” become rare.
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Frequently Asked Questions About Comma Before or After “But”
When do you put a comma before “but”?
Put a comma before “but” when it connects two independent clauses—two groups of words that each contain a subject and a verb and could each stand alone as complete sentences. Example: “I wanted to stay, but I had to leave.” If the second part cannot stand alone, no comma is needed.
When do you put a comma after “but”?
Put a comma after “but” only when it is immediately followed by an interrupter—a word or phrase (such as of course, unsurprisingly, or to be fair) that adds emphasis or tone but is not grammatically essential. Example: “But, of course, she already knew.”
Do you always need a comma before “but”?
No. A comma is needed before “but” only when both connected clauses are independent. When “but” connects a clause to a phrase or fragment—such as in “tired but happy” or “she tried but failed”—no comma is used.
Can you start a sentence with “but” without a comma?
Yes. Starting a sentence with “but” is grammatically acceptable, and no comma follows it unless an interrupter appears directly after “but.” “But he didn’t answer” is correct without a comma.
How do I know if a clause is independent?
Ask whether the clause could stand alone as a complete sentence. It needs a subject, a verb, and a complete thought. If you cover the part before “but” and ask whether the remaining words form a complete sentence—and then do the same for the words before “but”—both passing confirms two independent clauses.
Does the comma before “but” rule apply to other coordinating conjunctions?
Yes. The same rule applies to all FANBOYS conjunctions: For, And, Nor, But, Or, Yet, So. Use a comma before any of these when they join two independent clauses.
Is a comma required with “not only…but also”?
Only when both clauses are independent. “She not only wrote the report, but she also presented it” (two independent clauses—comma required). “She is not only smart but also hardworking” (not two independent clauses—no comma needed).
What is the most common comma error with “but”?
The most frequent mistake is adding a comma before “but” when the second element is not an independent clause. For example, “She was tired, but happy” is incorrect. The correct version is “She was tired but happy”—”happy” alone is not an independent clause.
