How to Use Commas

Commas keep ideas separate and provide clues about how phrases relate to each other. Most of the time, commas belong in predictable places, but it is not necessary to use one if it will cause confusion or make a sentence awkward. For example:

1. While I ate the plate grew cold and the food lost its taste.

Do I mean that I ate the plate? No, of course not. I need a comma or two in order to clarify what I mean here:

2. While I ate, the plate grew cold and the food lost its taste.

Do I need another comma?

3. While I ate, the plate grew cold, and the food lost its taste.

The punctuation in both sentences is correct. Choosing to use one or two commas depends on how closely I want to link the cold plate to the tasteless food. Sentence 1 indicates that the food lost its taste because the plate grew cold since there is no pause. Sentence 2 is more like a list, the pause indicates that the cold plate is not necessarily the cause of the tasteless food, yet the phrases have equal emphasis.

Commas also set apart non-essential phrases. A good test is how important the information is to the sentence. If the point is clear without the phrase, then it needs two commas to set it apart. For example:

1. While I ate, chewing slowly as I thought of other things, the plate grew cold and the food lost its taste.

Lists: A, B, and C—if there are three or more elements, use commas and the word “and.” For only two elements, use only the word “and.” For example:

• There was pizza, salad, fruit, and bread on my plate.
• There was pizza and bread on my plate.

Lists of adjectives: use a comma for descriptions not joined by a conjunction word. For example:

• There was hot, delicious pizza and warm, crusty bread on my plate.

Conjunctions: Words like “for,” “and,” “or,” “but,” “nor,” “yet,” and “so” need a comma before them when they connect two independent clauses. In other words, when they connect two complete sentences. For example:

• There was pizza and bread on my plate, but I still needed to get salad and fruit.

Do not use a comma if either phrase is not a complete thought. For example:

• There was pizza and bread on my plate but no salad or fruit.

Clauses: Use a comma before and after, just like this, to set apart extra information supporting the main point or after introductory words or phrases. For example:

• The pizza on my plate, a large slice, was growing cold.
• Darn, the pizza on my plate was growing cold.

Quotations: Use a comma between your own words and a quote. For example:

• As I ate my pizza I heard someone say, “Chew your food slowly,” yet I worried my food would grow cold.

Names: Use a comma in front of geographical names and titles in names. For example:

• The pizza place is located in Saint Paul, Minnesota.
• Ben Chau, PhD is an expert in food science.