Understanding what is a clause is essential to produce correctly-punctuated sentences. Daily Writing Tips shared this thorough yet simple explanation in one of their newsletters. Don’t forget to test your knowledge with the quiz at the bottom!

What Is a Clause?

A clause is a statement or a question that generally consists of a subject and a verb phrase and constitutes a complete thought. Sentences can consist of a single clause, but they often include two: a main, or independent, clause and a subordinate, or dependent, clause.

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Main Clause vs. Dependent Clause

A main clause can form a complete sentence. (The preceding statement is both a clause and a sentence.) A subordinate clause, by contrast, depends on a main clause to provide the primary proposition of the sentence, which is why it’s also called a dependent clause.

“Which is why it’s also called a dependent clause” is itself a dependent clause. One could write or speak that sequence of words on its own, and listeners and readers would understand that it pertains to the previous sentence. However, in formal writing, it’s best to link such constructions to a main clause with a punctuation mark—usually a comma, though a dash can also link a main clause to a dependent clause, as it does in this sentence.

Dividing Sentences with Two Main Clauses

A sentence may contain two main clauses; in this sentence, a semicolon separates the two main clauses, although a dash may also be employed. Note that the semicolon could be replaced with a period—the segments of the sentence that precede and follow the semicolon could be formatted as a separate sentence. The preceding sentence could also be divided into two: one sentence could be formed from the clause preceding the dash, and another could consist of the clause following the dash.

Using Colons in Clauses

The sentence preceding this statement shows another punctuation mark that can distinguish one main clause from another: the colon. Note, however, that in the sentence before this one, what follows the colon is a sentence fragment—“the colon” includes a subject but no verb phrase—so that sentence does not contain a main clause and a dependent clause.

Importance of Dependent Clauses in Written Communication

It’s a good thing for written communication that English allows—even encourages—dependent clauses. Otherwise, writing would consist solely of main clauses. A succession of main clauses causes reader fatigue. Engagement in a piece of text is enhanced by a variety of sentence structures. (I’ll stop annoying you with this string of main clauses now.)

Today’s Quiz

Question 1:

Which of the following sentences correctly uses a main, or independent, clause and a subordinate, or dependent, clause?

a) The game was quite intense, as the team fought hard.

b) I enjoy playing piano also it’s a good stress buster.

c) Tea is brewing; it will be ready in a few minutes.

d) The food was delicious, however, the dessert was too sweet.

Question 2:

Which punctuation mark should you use to link a main clause to a dependent clause?

a) a colon

b) a semicolon

c) a comma

d) a period

Question 3:

Which of the following punctuation marks is also appropriate for linking dependent clauses to a main clause?

a) a dash

b) a question mark

c) a hyphen

d) an exclamation point

Question 4:

Which of the following sentences appropriately represents the structure of a sentence containing both a main and a dependent clause?

a) I believe it’s going to rain, though the weather report portends clear skies.

b) The weather report portends clear skies; nonetheless, I believe it’s going to rain.

c) The weather report that portends clear skies; I believe it’s going to rain.

d) The weather report makes me believe it’s going to rain.

Question 5:

Which one of the following sentence structures is regarded as fatiguing for the reader?

a) a sentence containing only dependent clauses

b) a sentence containing both an independent clause and a dependent clause

c) a succession of sentences containing only independent clauses

d) a succession of sentences containing both an independent clause and a dependent clause

The correct answers are as follows:

1. a) The game was quite intense, as the team fought hard. (The dependent clause “as the team fought hard” is correctly attached to the independent clause “The game was quite intense.”)

2. c) comma (Commas are commonly used to link an independent clause to a dependent clause.)

3. a) dash (A dash can be used ito link a dependent clause to an independent clause.)

4. a) I believe it’s going to rain, though the weather report portends clear skies. (This sentence is structured correctly with the independent clause “I believe it’s going to rain” and the dependent clause “though the weather report portends clear skies.”)

5. c) a succession of sentences containing only independent clauses (According to the lesson, a succession of independent clauses causes reader fatigue.)

Section 6.52 in the Spotlight

The seventeenth edition of CMOS was the first edition to rule explicitly on whether “too” in the adverbial sense of “also” should be set off by commas. The rule applies also to “either,” which as an adverb can play a similar role in a sentence or clause.

The short answer is that commas are unnecessary but occasionally helpful for emphasis or clarity. We can find out what this means in practice—and why having a rigid rule isn’t a good idea—by starting with a simple example.

The first edition of the Manual, published in 1906, may not have addressed “too” or “either” by name, but it did have something to say about such words. Paragraph 132 ended with a suggestion that commas should not be used “ordinarily with such terms as ‘perhaps,’ ‘also,’ ‘likewise,’ etc.”—and offered a few examples in support of this.

Here’s the last one: “He was a scholar and a sportsman too.” Note the absence of any comma. And though it wasn’t featured in the examples, the word “either” would play the same role in such a sentence rewritten in the negative: “He wasn’t a scholar or a sportsman either.”

Whatever else you might think of that ancient example from the first edition, it does provide the basis for a rule—or in this case a sort of nonrule.

What Was That Rule Again?

Some people have tried to argue that whether to set off “too” (or “either”) depends on its relationship to the words in the sentence. According to this argument, a comma would be required in our original example if “too” applied to “sportsman” but not if it applied to the subject “He” (or to the sentence as a whole).

Or is it the other way around?

That’s a serious question, because such a rule would require an agreement between writers and readers on precisely how to interpret the presence or absence of a comma.

Let’s say there is such an agreement. Then the following sentence—with a comma before “too”—would mean that the subject “She” (let’s bring the answer into the twenty-first century) is not only a scholar but also an athlete, with the emphasis on “athlete”:

She is a scholar and an athlete, too.

Applying the same logic, removing the comma would alter the meaning. Without the comma, some previously mentioned other person or persons are scholars and athletes, and “She,” like that person or those people, is also a scholar and an athlete, with the emphasis on “She”:

She is a scholar and an athlete too.

You could extend this logic to “either” by rewriting the sentence in the negative: “She wasn’t a scholar or an athlete either.” That would put the emphasis on “She”; adding a comma would move the emphasis to “athlete”: “She wasn’t a scholar or an athlete, either.”

Makes sense, right? Yes, maybe—except there is no such agreement.

Context Is Everything

When it comes to making meaning, context is almost always more important than commas. This is particularly true with “too” and “either.” If your sentence is not entirely clear from context alone, revise until it is.

In the following example, it’s clear from context that “too” refers to “athlete”:

Maria’s academic achievements are well known, but she also excelled at track and field. Maria was a scholar and an athlete too.

When it comes to making meaning, context is almost always more important than commas.

But in this example of dialogue, the context makes it clear that “too” refers back to “Maria”:

“All my eleven kids got perfect grades while excelling at sports.”

“Maria was a scholar and an athlete too,” I reminded her, making a plug for my daughter.

In either case, a comma would have made no appreciable difference to the meaning, which is predetermined in both examples by the context.* (Again, you can make the examples negative to test “either.”)

Italics and Word Order

Where emphasis is important, and you don’t want to leave it to context alone, one option is to apply italics. Italics will help readers decode the intended meaning, or at least the intended emphasis. Add commas to the following examples if you like, but they won’t change the meaning of either version.

Maria was a scholar and an athlete too.

Maria was a scholar and an athlete too.

Another option that works well with “too” (but rarely with “either”) is to shift the placement of the adverb. In the following example, it is obvious that “too” applies to Maria:

Maria too was a scholar and an athlete.

Commas lend an additional dimension to this sentence:

Maria, too, was a scholar and an athlete.

Those commas, by drawing attention to the word “too,” emphasize the rhetorical shift implied by that word. Especially when “too” occurs midsentence, such commas may add a bit of clarity also.

Summing It Up

Some writers follow a simple rule: use commas with “too” and “either.” And because such commas don’t have the power to determine the intended meaning all by themselves, this approach is fine. Editors working with authors whose style depends on frequent, well-placed commas (in what is sometimes called close rather than open punctuation) should query before simply removing them.

But in general, Chicago favors a relatively spare, open approach to commas, omitting many commas that aren’t necessary for comprehension—including commas with “too” and “either.”

If that’s you too, then you won’t need those commas either.

In sum, the key to deciding when to use commas with “too” and “either”—and the spirit of the rule in section 6.52—is to leave them out by default. Then add them only rarely if at all—and only where a bit of extra emphasis or clarity seems warranted.

* It may go without saying, but the functionally similar word “also” is almost never set off by commas: “She was a scholar and an athlete also.” This is perhaps the strongest argument for not requiring commas with “too” and “either.”