AP® English Language and Composition · Big Idea 4 Style: Grammar, Mechanics, and Punctuation (Skills 7.C, 8.C)
7.C The Comma (STL-1.O)
A comma is a light joint: it can attach a leaning piece to a complete sentence, but it cannot hold two complete sentences together. Using it that way causes a comma splice.
Think of a comma as the weakest connector in the punctuation toolkit. It can join an incomplete piece, a leaning block like a dependent clause, an introductory phrase, or an appositive, onto a complete sentence that can stand on its own. What it cannot do is bolt two complete sentences together, because each one is already a standing structure, and a comma has no strength to bear that load. Try it and you get a comma splice: two independent clauses glued by a comma alone.
The comma's jobs split three ways. It joins a leaning element to a main clause. It separates items in a series so a reader knows where one item ends and the next begins. And it sets off extra information, like a name being addressed or a nonessential description, by wrapping or trailing it with commas. Each job answers a different question: does this piece need support, does this list need dividing, or is this chunk removable without wrecking the sentence.
This sits right next to the semicolon and the period in the unit, because all three solve the comma splice problem in different ways: a period makes two sentences, a semicolon treats both halves as equal and connected, and a comma only works if you also add a coordinating conjunction like and or but. Seeing the comma's limits is what makes the stronger joints make sense.
Key terms
- Comma splice
- An error where two independent clauses are joined by only a comma, with no conjunction.
- Independent clause
- A group of words with a subject and verb that can stand alone as a complete sentence.
- Appositive
- A noun or noun phrase set off by commas that renames or adds detail to a nearby noun.
- Series comma
- A comma used to separate items in a list, including the one before and or or in a three-item list.
Watch it explained
- How it worksHow do the comma's jobs split into joining, separating, and setting off?
- Worked exampleWalk me through Let's eat, Grandma and Let's eat Grandma and the two pictures they draw.
- Worked exampleShow me why The rain stopped, we went outside collapses, then four legal ways to repair it.
- Common mistakeWhy isn't a comma placed wherever you would pause if you read the sentence out loud?
- Going furtherWhat changes when a comma is added or dropped before the and in a three-item list?
Check yourself
End of topic.