Commas are used more frequently than any other punctuation mark. Like all other punctuation marks, use a comma to keep your readers from being confused. When readers see a comma, they know a slight pause comes at that place in the sentence, and they can tell how particular words or phrases relate to other parts of the sentence. Take a look at this sentence:

What's being said here? This sentence has entirely different meanings, depending on how commas are placed in it.

Using Commas with a Series

If you have a series of items, use a comma to separate the items. Take a look at this sentence:

How many vehicles were involved? With the following punctuation, you'd see that three vehicles were involved.

However, this punctuation shows that only two vehicles were involved.

Use a comma between two or more adjectives (words that explain or describe or give more information about a noun or pronoun) that modify a noun (the name of a person, place, thing, or idea):

If the first adjective modifies the idea expressed by the combination of subsequent adjectives and the noun, then you don't need commas. Look at this sentence:

Since central governments would be considered a single unit, you don't need to separate it from the adjective modifying it (stable) with a comma.

If you're using and, or, or nor to connect all the items in the series, don't use commas: