•When I watch movies, I like to eat popcorn.
•An appositive is a word or group of words that explains another word in a sentence.  Use commas to set off an appositive from the rest of the sentence.

•Mr. Lee, my favorite teacher, gave us extra homework today.

 

The comma is the punctuation mark most likely to cause angst. This is largely the result of the many different ways the comma is used. Sometimes, the comma indicates a pause that would occur if the sentence were spoken aloud. Other times, the comma separates grammatical components of the sentence. Finally, there are mechanical and stylistic uses of the comma that are simply conventional.

 

The presence or absence of a comma can change the meaning of a sentence—sometimes dramatically. In extreme cases, an erroneous comma can make a sentence mean the exact opposite of what the writer intended. A careful writer must be a careful user of commas.

 

You may need to learn a few grammatical terms to understand this one.

An independent clause is a unit of grammatical organization that includes both a subject and verb and can stand on its own as a sentence. In the previous example, "I went running" and "I saw a duck" are both independent clauses, and "and" is the coordinating conjunction that connects them. Consequently, we insert a comma.

If we were to eliminate the second "I" from that example, the second clause would lack a subject, making it not a clause at all. In that case, it would no longer need a comma: "I went running and saw a duck."

Example: "When I went running, I saw a duck."

A dependent clause is a grammatical unit that contains both subject and verb but cannot stand on its own, like "When I went running ..."

Commas always follow these clauses at the start of a sentence. If a dependent clause ends the sentence, however, it no longer requires a comma. Only use a comma to separate a dependent clause at the end of a sentence for added emphasis, usually when negation occurs.

Mrs. Clark asked if Amy would help.

Uncle Rob took us to Texas. 1

I ate pizza, a burger,and ice cream.