When the independent clause comes before the dependent clause, do you need a comma between them?

In this section, we'll review dependent and independent clauses and how to punctuate sentences that include include them.

Clauses can be divided into two kinds: dependent and independent. A dependent clause contains a subject and verb, but cannot stand on its own as a complete sentence; an independent clause includes a subject and a verb, and expresses a complete thought. An independent clause is a complete sentence in itself but may appear together with other clauses in compound or complex sentences. For example, "as soon as you get here" is a clause; it has a subject (you) and a verb (get), but it doesn't express a complete thought. Therefore it is not independent; it can't stand alone as a sentence.

On the other hand, "we will go out together" is an independent clause with a subject and verb, and it can stand on its own as a sentence. When joined together, as in "As soon as you get here, we will go out together," the phrase and clause create a sentence comprising an independent and dependent clause.

Another way to recognize dependent and independent clauses is to look for signal words. Signal words often appear before phrases and, once you're in the habit of looking for them, can alert you to a dependent clause. For example, the phrase "When it rains in Seattle," is a dependent clause. It has a subject ("it") and a verb ("rains"), but it does not express a complete thought. The word "When" is also another indicator that you are looking at a phrase. "When" is one of several signal words called a subordinating conjunction. Other subordinating conjunctions include: although, because, before, how, if, since, though, where, whether, and while.

How to join dependent and independent clauses

You can use a comma to join dependent and independent clauses. The comma indicates where one clause ends and another begins. In some cases, you won't need a comma if there is no confusion about the boundary of the clauses. Here are some examples:

• 1. When it rains in Seattle, I just want to move.
• 2. When it rains in Seattle I just want to move.
• 3. I just want to move when it rains in Seattle.

The use of a comma when a dependent clause comes before an independent clause (as in Example 1 above) is optional, particularly when joining two short clauses, but you'll most commonly see a comma used to separate the two clauses. However, that guideline is generally not applied when the sequence of phrases is reversed, as in Example 3.

How to join sentences

You have two choices when joining sentences—or two independent clauses.

• You can use a comma and an appropriate conjunction (e.g., and, but, or, nor, so, for, yet).
• Or you can use a semicolon.

Suppose you want to join the following sentences:

• 1. Using this authentic batch-style method, our chips are cooked in expeller-expressed oil.
• 2. This oil, unlike most oil, is high in antioxidant substances.

Joining sentences 1 and 2 together using the strategies outlined above, produces two possible options:

• 3a. Using this authentic batch-style method, our chips are cooked in expeller-expressed oil, and this oil, unlike most oil, is high in antioxidant substances.
• 3b. Using this authentic batch-style method, our chips are cooked in expeller-expressed oil; this oil, unlike most oil, is high in antioxidant substances.

In Example 3a, the writer uses the conjunction "and" with a comma and in 3b, a semicolon. Each has a slightly different rhetorical effect. With "and," the relationship between the oil and the antioxidant substances is explicit. In other words, the ideas have been combined in a way that makes it clear to the reader what the relationship is between the first and the second clauses.

The semicolon, on the other hand, is no less appropriate, but the reader has to judge from the context what the relationship is between the ideas expressed in each clause since a semicolon can suggest several things, from combination and contrast to simply giving additional information. For example:

• He prefers sports cars; I prefer sedans.

Here a semicolon joins two sentences that express contrast between two people's preferences. This relationship between clauses could be made even more explicit, however:

• He prefers sports cars, but I prefer sedans.

Conjunctions and semicolons are both options for joining sentences, but each produces a different rhetorical effect. Conjunctions make the relationship between sentences explicit, while semicolons require the reader to determine the relationship from context.

Academic writing expresses complex ideas and, as a result, often requires sentences that are equally complex. For this reason, it's not uncommon to see comma splices—joining two independent clauses with a comma—in your work as the demand for complexity increases. Below you'll find ways to recognize and correct these kinds of errors.

In most cases, joining two independent clauses (i.e., clauses that can stand alone as complete sentences) by a comma creates a comma splice.

• 1. The dialogues between Clarence and Mariano advance the novel's plot, the narrator's interventions, on the other hand, are extraneous.

In this example, the two ideas expressed are clearly related, as the author wishes to contrast the characters' dialogue with the narrator's. However, the sentence contains a comma splice because the clauses on both sides of the comma are independent clauses:

• a. The dialogues between Clarence and Mariano advance the novel's plot.
• b. The narrator's interventions, on the other hand, are extraneous.

In other words, the two sentences above can stand alone as complete sentences. Joining them with a comma results in a comma splice.

Correcting comma splices

To correct a comma splice, take a look at the clauses that make up the sentence. Be sure that each sentence includes only one independent clause and the rest dependent clauses.

A dependent clause cannot stand alone as a sentence. Like an independent clause, it has a subject and a verb. It may not, however, express a complete thought and may begin with a signal word called a subordinating conjunction. The chart below outlines common coordinating and subordinating conjunctions discussed in this section.

Using the chart above, we can correct the comma splice from the previous sentence in several ways:

• make one of the independent clauses into a dependent clause,
• separate the independent clauses into two sentences, or
• link the two independent clauses with a semi-colon.

Fragmented sentences

A final problem related to sentence structure concerns sentence fragments. Sentence fragments occur when a writer punctuates a phrase as if it could stand alone as a sentence, for example:

• 1. There's no question about trust. Because everyone is bound by it.

"Because everyone is bound by it" is not a complete sentence, but a dependent clause. To correct the fragment, you could join the dependent clause to the independent clause (or the main clause). For example:

• 2. There's no question about trust because everybody is bound by it.

The best way to test whether or not you have a sentence fragment is to evaluate whether the clause expresses a complete thought. If not, then look for signal words that could indicate the beginning of a dependent clause. If you have a clause that does not express a complete thought and begins with a signal phrase, then you're likely looking at a sentence fragment.

In this section, we reviewed dependent and independent clauses and the punctuation used to join them.

Back to Grammar in College Writing

"Effective use of the comma involves good judgment, with ease of reading the end in view."

—The Chicago Manual of Style

How can such a little punctuation mark cause so much trouble for both English language learners and native speakers? There are so many cases where commas are needed (such as with non-restrictive adjective clauses or multiple adjectives), where it's your choice to use them or not (such as with the serial comma), and where they shouldn't be used (such as with restrictive adjective clauses). Also, as more of us text and write on our computers or other mobile devices, comma usage seems to be dwindling.

So where does this leave students who are trying to learn the correct way to use commas? Luckily, there are a few basic rules that will still be considered correct for a long time to come.

Independent Clauses

Rule #1: Comma Needed

If two independent clauses are joined by a conjunction (and, but, so, or), use a comma. This is true whether the subject is the same or different in both clauses. This is also true for imperative sentences where the subject is dropped.

• They are just finishing up the report, so they are almost ready to present it to the boss. (same subject)
• She didn't like the restaurant I recommended, but her husband really enjoyed it. (different subjects)
• Discuss these questions with your group, and be sure to take notes during the discussion. (imperative verbs)

Rule #2: No Comma Needed

If the conjunction is only joining parts of the independent clauses (i.e., the second subject and/or verb is dropped because it is the same), no comma should be used. However, if you teach higher-level students, you may want to point out that a comma could be added if the first clause is quite long (for the sake of readability—see the conclusion below).

• We finished the report and presented it to the boss.
• They want to go skiing and snowboarding over the holidays.
• I'll call him tonight or email him tomorrow.

Rule #3: Comma Optional

If the two independent clauses are very short, you can omit the comma. As noted in the intro, the trend nowadays is to omit the comma wherever possible. Note that students might be wondering how they can tell if a clause is 'short.' Remind them that if they're in doubt, use a comma because that will always be considered correct. In fact, you may not want to mention this rule to your lower-level students—it might cause unnecessary confusion.

• I cooked and she cleaned.
• Lisa made cookies and Pedro baked a cake.
• Raise your right hand and repeat after me.

Dependent Clauses

Rule #4: Comma Needed

If the dependent clause comes before the independent clause, use a comma.

• Even though it was raining, I didn't bring an umbrella.
• Because you reminded him, he brought the necessary documents to the meeting.
• If she calls in sick, I will take over for her.

Rule #5: No Comma Needed

If the dependent clause comes after the independent clause, don't use a comma.

• I didn't bring an umbrella even though it was raining.
• He brought the necessary documents to the meeting because you reminded him.
• I will take over for her if she calls in sick.

Conclusion

Tell your students they can feel confident that their written work will always be correct if they follow the rules above. But make sure they also understand that some commas are optional (or can be added or deleted for readability even when it's not the usual rule). They will come across instances where the rules aren't followed to a T (and that's usually okay). The good news is that even if they make a mistake with the rules above, it won't always be considered wrong. If there is another comma case you'd like me to blog about, just leave a comment below! 

Source: The Chicago Manual of Style, 16th edition, sections 6.16–6.32