But is what we call a coordinating conjunction; it connects groups of words that are considered equal in rank.
Other common coordinating conjunctions are and, for, or, nor, so and yet.
Some readers have questioned whether to always use a comma before but. The answer: No, not always.
Can you spot what’s lacking in the second of each of these examples?
My report was late, but my boss accepted it anyway.
My report was late but was accepted anyway.
I’d like to go to the art fair, but I don’t have extra money to spend.
I’d like to go to the art fair but don’t have extra money to spend.
Robert was supposed to come to work early, but he forgot.
Robert was supposed to come to work early but forgot.
The first sentence of each set consists of two independent clauses. In other words, each clause separated by but and a comma has a subject and a verb; each could stand alone as a sentence:
My report was late. My boss accepted it anyway.
I’d like to go to the art fair. I don’t have extra money to spend.
Robert was supposed to come to work early. He forgot.
In the second sentence of each set, what follows but has no subject:
… but accepted it anyway.
… but don’t have extra money to spend.
… but forgot.
To decide whether to precede but with comma, consider what follows it. If the phrase has a subject and a verb, insert a comma. If not, leave it out.
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