Whether or not you put a comma before and depends on how you’re using and. There’s no single rule that applies to all situations. You usually put a comma before and when it’s connecting two independent clauses. It’s almost always optional to put a comma before and in a list.
Comma Before And in Lists
A lot of people have strong feelings about putting a comma before and in a list. Exactly why this particular quirk of comma usage stirs such passions is hard to say; it’s just one of those things. If you’ve ever heard someone arguing about serial commas or Oxford commas, this is what they were talking about.
Let’s say your dog has so many great qualities that you just have to tell the world. When you list your dog’s qualities, you have to use a comma after each quality you list except the one that comes immediately before and. That comma is optional.
The sentence is correct with or without the comma before and. (There are a few exceptions that require you to use the Oxford comma in a list, but they are pretty rare.) Just be consistent. Don’t switch back and forth in the same document between using the Oxford comma and not using it.
By the way, this rule only applies to lists of three or more items. You should not use a comma before and if you’re only mentioning two qualities.
This is true for proper names, ordinary nouns, verbs, or anything else.
Comma Before And That Joins Two Independent Clauses
The word and is a conjunction, and when a conjunction joins two independent clauses, you should use a comma with it. The proper place for the comma is before the conjunction.
The sentence above contains two independent clauses (highlighted in green), so it requires a comma before and. (By the way, you can tell they’re independent clauses because each one could stand on its own as a complete sentence.)
Let’s look at another example.
Once again, we have two independent clauses: It’s cold outside I can’t find my coat. Therefore, we need a comma before and.
Don’t use a comma before and when one of the clauses it’s connecting is a dependent clause.
The first clause, Sam tossed the ball could stand on its own as a complete sentence, which means it’s an independent clause. But the second clause, watched the dog chase it, can’t stand by itself as a complete sentence. That means it’s a dependent clause, so we should not use a comma before and.
But wait! There’s an exception. (Isn’t there always?) When you have two independent clauses joined together by and, most style guides say that it’s OK to leave the comma out as long as the two independent clauses are very short and closely connected. Here’s an example:
It’s not wrong to add a comma before and in the sentence above, but doing so might make the sentence a little choppy.
Want to learn about other ways to use a comma? Check out our general guide to comma usage.