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.
However, if your organisation advocates the Oxford Comma, use a comma. Also, if breaking convention makes your text clearer, then break convention.
Comma before AndThis 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 ClausesWhen 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):
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 ItemsWhen there are two items in a list, there is no need to separate the list items with a comma.
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.
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.
WHAT IS A COMPOUND SENTENCE?
A sentence made up of two simple sentences (or independent clauses as they're really called) is known as a compound sentence. The conjunction that joins the two halves of a compound sentence should be preceded by a comma.