Question

When there is a ‘but’ between two clauses, when do you need a comma and when not?

Example (the context is narrative, not formal):

 1.  I walked down the same street, but this time I turned left.

Here, the comma is needed because it is a coordinating conjunction between two independent clauses, right?

2.  I walked down the same street but, this time, I turned left.

Here, two commas set off a parenthetical phrase, yes? Do you still need the comma after the “but”? But that looks cluttered and hard to read!

3.  I walked down the same street but this time I turned left.

This seems perfectly clear and legible. Is it necessarily wrong?

(I do get the sense that comma usage, like other punctuation, is shifting toward less-is-more simplicity.)

Answer

These are the three rules that I follow for punctuating coordinating conjunctions, such as ‘and’, ‘or’, ‘but’:

1.  Where two independent clauses are joined by a coordinating conjunction, put a comma at the end of the first clause,

He read the question, and he wrote a reply.

Note: You may omit the comma if you regard both the clauses as quite short, eg: He read and he wrote.

2.  Where two independent clauses are joined by a coordinating conjunction and the subject of the first clause and the subject of the second clause are different, put a comma at the end of the first clause

He thought quickly about the question but still did not write a reply.

[No comma because ‘he’ is the subject of ‘thought’ and of ‘write’, and the second subject is not explicit.]

He saw that she was asking a question, but was prepared to leave it unanswered.

[Use a comma because the subject of ‘was asking’ and ‘was prepared’ is different, and the second subject is not explicit. The use of the comma avoids confusion.]

He thought about the question, but she formulated an answer herself.

[Use a comma because the subjects of ‘thought’ and ‘formulate’ are different.]

3.  Do not use a comma after ‘but’.

Let’s look at your sentences:

1.  I walked down the same street, but this time I turned left.

Q: Here, the comma is needed because it is a coordinating conjunction between two independent clauses, right?

A: Yes, you are following rule 1 above.

2.   I walked down the same street but, this time, I turned left.

Q:  Here, two commas set off a parenthetical phrase, yes? Do you still need the comma after the “but”? But that looks cluttered and hard to read!

A:  Yes, you are following rule 1 above because, I presume, you regard both clauses as quite short.

You are breaking rule 3 above but with good reason: your deictic emphasis requires the use of parenthetical commas.

3.  I walked down the same street but this time I turned left.

Q:  This seems perfectly clear and legible. Is it necessarily wrong?

A:  You are following rule 2 above.

This useful explanation was supplied by Corné Janse van Rensburg in a PEGforum thread Grammar gremlin – but me no buts! on Tuesday, 22 April 2025.

Posted Apr 22, 2025 at 19:40

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