Write well. Write often. Edit wisely.
A reader asked about commas with subordinate—also known as dependent—clauses. Because the topic covers several issues and because I was already working on one of the sub-topics for another article, I thought I’d answer the question in an article rather than in the comment section.
I’m having trouble knowing when to put a comma before a subordinate clause. For instance, why would there not be a comma before after in The police officer pleaded guilty to careless driving after crashing his car into a fence, yet there would be a comma before after in the sentence The police officer, after cashing his car into a fence, pleaded guilty to careless driving. Since you can move the “after . . .” part of the sentence around, why is it considered essential?
This is a great question because it delves into specifics of comma use with dependent clauses.
Because there are several types of dependent clauses—adjective, adverbial, and noun—this topic could get wordy if I tried to cover all of them. I’m going to focus on adverbial clauses since they’re usually the ones that cause the most problems and because the example in the reader’s question uses an adverbial clause.
A few details first—
An independent or main clause can stand alone as a sentence. It has a subject and a verb and conveys a complete thought.
The ball belongs to Alice.
The ball rolled down the hill.
The ball was red.
A dependent or subordinate clause can’t stand alone as a sentence. It does have a subject and a verb, but it doesn’t convey a complete thought. It depends on other sentence elements (typically an independent clause) to give it meaning.
Because the ball belonged to Alice
After the ball rolled down the hill
Since the ball was red
These are incomplete sentences because they don’t convey a complete thought.
Because the ball belonged to Alice, what?
After the ball rolled down the hill, what happened?
Since the ball was red, what?
An adverbial clause often starts with a subordinating conjunction. A short list of subordinating conjunctions:
A subordinate clause that stands alone is a sentence fragment. Students are taught to not use sentence fragments, but fiction writers use them all the time for effect and rhythm.
“Why’d you steal the code?”
“Because I can.”
Yeah, I planned on heading home. After I finished what I came to do.
While we can use dependent clauses as sentence fragments, most of the time we don’t. We usually pair them with at least one independent clause and create sentences.
The dependent clause can come before the independent one, after it, or it can come in the middle of it, interrupting the independent clause. Comma use is partly dependent upon where the dependent clause falls in relation to the independent clause.
Independent clauses often come first in our text, but putting dependent clauses first gives us variety in sentence construction.
Dependent Clause Before Independent Clause
When an adverbial dependent clause comes before the independent clause, we put a comma after the dependent clause (between the clauses). We don’t have to give any consideration to the topic of essential or nonessential—when the dependent clause comes before the independent, use a comma to separate them.
When I saw the destruction, I cried.
After the ball, Cinderella had to run home.
Although he turned down the job, the company did pay his travel expenses.
After crashing his car into a fence, the police officer pleaded guilty to careless driving.
Okay, that was the easy one. Let’s look at the next construction.
Dependent Clause After Independent Clause
When a dependent clause (we’re still talking adverbial clauses beginning with a subordinating conjunction) comes after the independent clause, most of the time there is no comma.
I cried when I saw the destruction.
Cinderella had to run home after the ball.
The police officer pleaded guilty to careless driving after crashing his car into a fence.
The company did pay Mark’s travel expenses, although he turned down the job.*
~ * There is a comma in the fourth example because the dependent clause begins with although, an adverb of concession. The adverbs of concession set up contrast clauses. Adverbs of concession include though, although, even though, and whereas. Use commas to introduce dependent clauses beginning with these words, even when the independent clause comes first.
She said it boldly, although I didn’t believe her.
My mother put on her dress, though it was still covered in mud.
John got out after six months, whereas Martin had to serve his full two-year sentence.
~ While, when it means as, is simply a subordinating conjunction. However, when while means whereas, it is being used as an adverb of concession and would be preceded by a comma after an independent clause. Think contrast.
The delivery guy waited in the pouring rain while [as] the little boy counted out his pennies.
The delivery guy waited at the door, while [whereas] his supervisor waited in the dry car.
~ The subordinating conjunction because, when it begins a dependent clause after an independent clause, usually gets no comma. Yet there are two instances when because is preceded by a comma in this sentence position.
First, when the independent clause contains a negative verb. We use commas in such sentences to eliminate possible confusion.
She didn’t run toward the house because she was afraid.
Without a comma, this sentence could be read two ways. But the reader has no way of knowing which reading is correct.
Either she didn’t run toward the house due to her fear (because she was afraid, which is likely what we want to say) or she didn’t run toward the house not because she was afraid, but for some other reason, a reason not mentioned in this sentence. If a reason other than fear was involved, go ahead and spell that out.
She didn’t run toward the house because she was afraid, but because she was eager to meet the ghost.
But if you want the first meaning, using because to mean due to her fear, adding a comma lets the reader know the reason for not running was because of her fear.
She didn’t run toward the house, because she was afraid.
The same reasoning is true for the next example.
Larry couldn’t grab all the marbles because they’d rolled down the hill.
Without a comma, this could mean Larry couldn’t grab all the marbles not because they’d rolled down the hill, but because of another reason altogether.
Larry couldn’t grab all the marbles because they’d rolled down the hill, but because the two little boys snatched them up.
But if you want the other meaning, Larry not being able to grab them because they rolled down the hill, use a comma before because to show this.
Larry couldn’t grab all the marbles, because they’d rolled down the hill.
The second exception for using a comma before because is when the cause in because could be paired with the wrong element, creating confusion for the reader.
Lauren suspected her brother-in-law robbed the bank because she had seen his mask in his car. X
Lauren suspected her brother-in-law robbed the bank, because she had seen his mask in his car.
Without a comma, this says that Lauren suspected that her brother-in-law robbed the bank on account of her seeing his mask, as if her seeing it led to his actions.
With the comma, the sentence says that she suspected him because she’d seen the mask.
Although I’ve marked the first sentence with an X, you could actually intend to say it with that meaning.
~ Use a comma to separate the dependent clause from the independent when it follows the independent one if the dependent clause is nonessential. Keep in mind, however, that many dependent clauses will be essential and will not require a comma.
Determining if the dependent clause is essential or nonessential can be tricky, but for nonessential in this construction, think parenthetical. If you could set the dependent clause apart from the independent clause by using a dash or parentheses—if it makes sense to do so and it is your intention to do so—you can also use a comma. When you use the comma (or dash or parentheses), you are declaring the dependent clause nonessential.
Showing that a clause is nonessential may be easier to do if you adjust the word choices.
Dexter went to jail after ten years on the run. (essential)
Dexter finally went to jail, after ten years on the run. (nonessential)
Dexter finally went to jail—after ten years on the run.
The original sentence says that Dexter went to jail after being on the run for ten years. The next two say that Dexter finally went to jail—it happened to be after ten years on the run, but the thrust is that he finally went. The word choices and use or non-use of the comma give meaning to the sentences.
What’s important here is that the writer has a choice and the choice will direct the meaning of the sentence. This is not an instance when you must use a comma, as you do when naming a spouse—My husband, Zane, is not a cowboy. You choose comma or no comma, nonessential or essential, depending on what you want the sentence to say. (Keep in mind that we’re still looking at dependent clauses after independent ones.)
A couple more examples—
Lana gave up looking before she found her sister. (essential)
Lana gave up looking ten years ago, before she discovered her sister was actually her mother. (nonessential)
Lana gave up looking ten years ago (before she discovered her sister was actually her mother).
Frances gave me her fork after the dog licked it. (essential)
Frances gave me her fork, after she let the dog lick it. (nonessential)
Frances gave me her fork—after she let the dog lick it.
Dependent Clause Within Independent Clause
A dependent clause can be nestled inside an independent clause. When a dependent clause is within the independent one, it’s an interrupter. An interrupter simply breaks the flow of a sentence, and there are many different kinds, not just dependent clauses. A single word, a phrase, or a clause can interrupt an independent clause, and interrupters include adverbs, participial phrases, absolute phrases, nonessential clauses, appositives, digressions, parentheticals, commentary, and asides. Any time these items interrupt a sentence—interrupt an independent clause—they are nonessential elements and need to be separated from the independent clause with punctuation.
We typically use commas both before and after most interrupters, yet you could use dashes or parentheses.
The man, breathing heavily, couldn’t call out for help.
Elton and Carl, recklessly and without warning, jumped off the roof.
Tina, surprisingly, didn’t faint.
Bettina, the strong one, did faint.
My best friend, Jilly, is coming for the weekend.
Tennessee and Georgia, because they couldn’t agree on water rights, went to war.
The police officer, after crashing his car into a fence, pleaded guilty to careless driving.
The information between the commas could be lifted out of the sentences and these sentences would still make sense in terms of both grammar and meaning. Would still be true. That is, taking out the dependent clauses would not negate the other parts of the sentence. The information between the commas is nonessential. The information may add details, but taking it out wouldn’t change the major thrust of the sentence or have readers trying to figure out what was going on. The sentences without the nonessential words, phrases, and clauses can stand on their own.
Note: Some sentences can be tricky. While it may seem obvious that the examples listed above require commas, do note that some sentences work both with commas and without; the difference is in their meanings. (This note has more to do with the differences between nonessential and essential than with dependent clauses and commas, yet since this topic is related, I’m including some details here.)
The pitcher, who had played ball as a boy, joined the senior circuit.
The pitcher who had played ball as a boy joined the senior circuit.
Both of these sentences are correct, but they have different meanings.
The first is talking about the pitcher, one who had been mentioned before or the only one around—maybe the one standing on the pitcher’s mound. The information about him playing ball as a boy does not identify the pitcher—it simply gives us more information about the man we have already identified as the pitcher.
In the second sentence, the information about one of the pitchers playing ball as a boy identifies which pitcher we’re talking about. It’s info essential to identify the pitcher.
This article covered a lot of detail. Keep in mind that while we were looking at commas with dependent clauses, we were specifically looking at adverbial clauses beginning with subordinating conjunctions.