When to Use a Comma before a Conjunction
The Quick Answer
When to use a comma before a conjunction.If you're merging two sentences into one with a conjunction, then use a comma before the conjunction (e.g., I like fish, and I like chips.

With lists, if there are just two list items, don't use a comma before the conjunction. With three or more, use a comma if you're an American.
- Fish, chips, and peas
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- Fish, chips and peas
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However, if your organization advocates the Oxford Comma, use a comma. Also, if breaking convention makes your text clearer, then break convention.
Comma before And
This page is about when to use a comma before a conjunction (i.e., a word like and, or, and but).Unfortunately, there is no simple rule like: always use a comma before and or never use a comma before and.
Use a Comma to Join Two Independent Clauses
When two standalone sentences (or independent clauses) are joined together using a conjunction (e.g., and, but, or), the conjunction should be preceded by a comma.Examples (the conjunctions are shaded):
- Our team was given 2 minutes' notice, but theirs had been training for weeks.
- I have spoken to Sarah, and she has confirmed the delivery date.
- I have spoken to Sarah, and confirmed the delivery date.
- We eventually found the cave, but Jack was not there.
- We built the hut in an hour and then painted it.
The conjunction and should not be preceded by a comma in this example because confirmed the delivery date is not a complete sentence, i.e., it is not an independent clause. This is just a list with two list items: spoken to Sarah and confirmed the delivery date.)
Don't Use a Comma to Join Two List Items
When there are two items in a list, there is no need to separate the list items with a comma.Examples:
- Fish and chips
- She would only eat ham and eggs.
- I have never been to London, or Paris.
With Three List Items, Use a Comma If You're an American (or an Advocate for the Oxford Comma)
When there are three or more list items, things start to get complicated. There a two conventions. Generally speaking (more on this below), Americans will use a comma, but Brits won't.Examples:
- Fish, chips, and peas
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- Fish, chips, and peas
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- Fish, chips and peas
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- I have never been to London, New York, or Paris.
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The Oxford Comma causes great debate amongst grammarians. The bottom line is this: use the convention that will least annoy your boss (or readers) and then be consistent throughout your document.
Read more about commas in lists.