In today’s post, we’ll be going over one of the most common ways in which we use commas: to separate grammatical parts of sentence. Before we get started, however, we’re going to take some time to go over three terms that will be important to understand for today’s post:
Independent clause: a set of words that contains a subject and a verb and can stand on its own as a complete sentence.
Example: “John went to the coffee shop.”
Dependent clause: a set of words that contains a subject and a verb but cannot stand on its own as a complete sentence.
Example: “While we wait for the plane to arrive“, I’ll make a few calls.“.
Coordinating conjunction: a word that joins words, group of words, or independent clauses of equal rank together (e.g., “and,” “but,” and “so”)
Example: “I like strawberries and blueberries.”
Example: “Kate likes cookies, but she dislikes cake.”
Example: “Michael was eager to start driving, so he took his G1 test on his 16th birthday.”
When we use commas to separate grammatical parts of sentences, we need to think about where independent clauses, dependent clauses, and coordinating conjunctions are placed in sentences.
Case #1: When a sentence contains two independent clauses, place a comma before the coordinating conjunction
“John went to the coffee shop, but he forgot to go to the grocery store.“
In this sentence, “John went to the coffee shop” and “he forgot to go to the grocery store” are independent clauses. The “but” is a coordinating conjunction that joins the two clauses. For this reason, we place a comma right before “but.”
However, if the independent clauses are short, you can leave the comma out.
“Lily walked to the restaurant and James drove.“
Case #2: If a sentence contains only one independent clause and no dependent clauses, don’t insert a comma before the conjunction.
“Do you want an apple or an orange?”
“Do you want an apple, or an orange?”(incorrect)
Because this entire sentence makes up a single independent clause, don’t place a comma before “or.”
Case #3: If a dependent clause comes before an independent clause in a sentence, place a comma between the clauses
“While we wait for the plane to arrive, I’ll make a few calls.“
In this sentence, “While we wait for the plane to arrive” is a dependent clause and “I’ll make a few calls” is an independent clause. As a result, we place a comma between the two clauses.
Case #4: If the dependent clause comes after the independent clause in a sentence, don’t include a comma
“I’ll make a few calls while we wait for the plane to arrive.“
In this case, the dependent clause (“While we wait for the plane to arrive”) comes after the independent clause (“I’ll make a few calls”), so we leave the comma out.
Case #5: When a sentence begins with a dependent clause that applies to two independent clauses that follow it, insert a comma after the dependent clause.
“If you want to go to the zoo, you need to eat your breakfast and your sister needs to take a shower.”
In this case, the writer is saying that two things need to happen if the reader wants to go to the zoo: the reader needs to eat breakfast and the reader’s sister needs to shower. In other words, the sentence begins with a dependent clause (“If you want to go to the zoo”) that applies to both independent clauses that follow it (“You need to eat your breakfast” and “your sister needs to take a shower”). For this reason, we place a comma right after “zoo.”
Note that we could also place a comma between the two independent clauses without making the sentence ungrammatical:
“If you want to go to the zoo, you need to eat your breakfast, and your sister needs to take a shower.”
However, adding the comma would change the meaning of the sentence. The sentence would no longer say that there are two things that need to happen if the reader wants to go to the zoo. Instead it would say that there is one thing that needs to happen if the reader wants to go to the zoo (i.e., the reader needs to eat breakfast). In this case, the reader’s sister needs to shower regardless of whether or not the reader wants to go to the zoo. That is, the dependent clause (“If you want to go to the zoo”) applies only to the first independent clause (“you need to eat your breakfast”).
Case #6: When a dependent clause occurs between two independent clauses and applies only to the second, place commas around the dependent clause.
“Rachel decorated the cake quickly, and when Matt saw it, he knew that she hadn’t spent much time on it.“
Here we have a dependent clause (“when Matt saw it”) that’s sandwiched between two independent clauses (“Rachel decorated the cake quickly” and “he knew that she hadn’t spent much time on it”). In this case, the dependent clause applies only to the second independent clause: It’s because Matt saw the cake that he knows that Rachel didn’t spend much time on it. However, it isn’t because Matt saw the cake that Rachel decorated it quickly. For this reason, “when Matt saw it” applies only to “he knew that she hadn’t spent much time on it.” As a result, we place commas before and after the dependent clause.
Have any lingering questions about how to use commas to separate parts of sentences? Leave us a note in our comments section below and we’ll do our best to incorporate your questions into one of our upcoming posts.
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