If you have two independent clauses (that is, two thoughts that could stand alone as sentences) and they're joined by but, or, yet, so, for, and, or nor (use the mnemonic boysfan to help you remember), join them with a comma:

The exception: You may eliminate the comma if the two independent clauses are short and if the sentence would still be clear without the comma. For example:

If you have a simple sentence with a compound verb, don't put a comma between the verbs:

Using Commas with Quoted Material

If a quoted sentence is interrupted by words such as he said or she replied, use commas in this way:

The first comma goes before the closing quotation mark and the second comma goes before the beginning quotation mark.

If the words being quoted make up a question or an exclamation, don't include a comma:

Using Commas with Clauses, Phrases, Appositives, and Introductory Words

Use commas to set apart clauses (groups of words that have a subject and a predicate), participle phrases (see Chapter 8), and appositives (words or phrases that give information about a noun or pronoun) that aren't necessary to the meaning of the sentence.

Take a look at this sentence:

If you took out the clause the only one who works in the deli at Sam's Supermarket, you'd still have the same essential parts of the sentence. You don't need to know where the man works in order to learn his hair and eye color. (The nonessential part of this sentence is called a nonrestrictive clause. See Chapter 8 for more information.) Here's another way of looking at it: If you can take out the part in question (the part you're questioning for commas) and the sentence still makes sense, then you should use the commas. Now look:

In this case, if you removed who works in the deli at Sam's Supermarket, you'd have The only man was arrested for stealing four grapes and five apples. That isn't the meaning of the original sentence. Remember: If you need the extra words for the meaning, you don't need the commas.

Commas are also used after introductory words such as exclamations, common expressions, and names used in direct address that aren't necessary for the meaning of a sentence. If you have words that begin a sentence and you could understand the sentence without them, use a comma to separate them from the rest of the sentence. For example:

A comma is also used before these same types of words and phrases when they appear at the end of a sentence, as long as they're not necessary for the meaning:

Use commas around words that interrupt a sentence (these words are called parenthetical expressions), as long as the words aren't necessary for the meaning:

Use a comma after an introductory verbal (a verbal is a participle, gerund, or infinitive) or verbal phrase:

Use a comma after an introductory adverb clause. (An adverb clause is a group of words that has a subject and a verb, and describes a verb, adjective, or other adverb.) For example:

Using Commas in Addresses

When writing out a mailing address as text (not on separate lines), put a comma between the person's last name and the start of the street address, then after the street address, then between the city and the state. Don't put a comma between the state and the zip code. For example:

If you're putting address information on separate lines, use a comma only between the city and state:

If you mention a city and state in text, put commas around the state:

The same is true if you mention a city and country; put commas around the country:

Using Commas in Dates

Put a comma after the day of the week (if you've stated it), the day of the month, and the year (if the sentence continues):

If you're writing only the day and month or the month and year, no comma is necessary:

Using Commas in Letters

Put a comma after the greeting (salutation) of all friendly letters and the closing of all letters:

Using Commas with Titles or Degrees

If a person's title or degree follows his or her name, put commas after or around it:

Using Commas with Long Numbers

Using commas helps readers understand long numbers more easily. If, for instance, you read the number 1376993, you'd have to stop, count the numbers, and then group them in threes before you could understand the number. Using commas to divide the numbers makes for quicker interpretation: