Learn the answers to frequently asked questions about commas in this post, which is part three in our blog series about using commas.Tweet
What is a Clause?
A clause, in terms of sentence structure, is a group of words that contains a subject and a predicate. Every complete sentence must contain at least one clause; however, many sentences contain multiple clauses. A subject is what or who the sentence is about. A predicate is something that describes the subject or states what the subject is doing. For example, in the sentence “Tommy ran,” Tommy is the subject and “ran” is the predicate stating what he is doing. Many of the most common confusions about comma usage have to do with connecting clauses within a single sentence. Two types of clauses are dependent clauses and independent clauses. We’ll discuss each one with respect to comma usage below.
All clauses contain a subject and a verb (also called a predicate). A dependent clause contains both of these elements, but does not express a complete thought, and therefore is not a complete sentence. An example of a dependent clause is, “when I get home” (this is an example of an adverb clause) or “whose writing I have read” (an example of a noun clause).
As you can see, a dependent clause is a sentence fragment rather than a full sentence. Many dependent clauses include a marker either preceding or following the clause, indicating that it is dependent. These markers indicate that there is more information necessary to complete the thought beyond the first clause (the first subject and predicate phrase) stated. Such markers include words like “when,” “after,” or “instead of.” For example, in the sentence “When Mark went to the store, he found his favorite ice cream,” the clause “When Mark went to the store…” is a dependent clause.
Independent clauses are made up of both a subject and a verb (a predicate), so they form a complete thought. An independent clause is a complete sentence by itself. Conjunctions such as “and,” “but”, and “or” often precede independent clauses, to connect them to the previous thoughts.
There are also independent clause markers — such as “also,” “consequently,” “however,” “furthermore,” “moreover,” “nevertheless,” and “furthermore” — that precede an independent clause. Independent clause markers form a complete sentence with that independent clause. For example, both the phrases “Mary went to the store” and “Furthermore, Mary went to the store” are both independent clauses and complete sentences.
Do you need to use a comma to connect clauses in a sentence? It depends on what type of clauses they are.
Connecting Independent Clauses
Examples: “…, and more importantly, …” & “…, but rather, …”
Commas precede and follow coordinating conjunctions (such as “and,” “but,” and “or”) that connect two independent clauses. Adverbs such as “importantly,” “significantly,” or “especially” can be added to these coordinating conjunctions to modify the clause that follows it. For example, consider the phrases, “and more importantly,” and “but especially.”
For example, review the following sentence: “He passed the test, and more importantly, he passed the class.”
Another example is the sentence: “He didn’t want to go to the store, but rather, he wanted to go to the movie instead.”
Note that, in both sentences, the clauses are independent clauses (“he passed the test” and “he passed the class” in the first sentence, as well as “he didn’t want to go to the store” and “he wanted to go to the movie instead” in the second sentence). As independent clauses, they could each stand alone as independent sentences.
Independent Clause Marker Words (for example, “also,” “however,” “further,” “therefore”)
❌ No Comma
On the other hand, a comma should not be used when the independent clause is preceded by an independent clause marker word. Examples of these types of marker words are: “however,” “also,” “furthermore,” and “therefore.” Independent clause marker words are essentially, any word that could be left off of the beginning of the sentence without resulting in that sentence being incomplete.
When the second independent clause in a sentence is followed by an independent clause marker, you can use a semicolon to separate the first and second independent clauses. When a comma is mistakenly used in these instances instead of a semicolon, this is a grammatical error known as a “comma splice.”
You can see this convention at work in the following example: “I wanted to go to the store before noon; however, I wanted to make sure to pick the kids up from daycare on time.” Note that both parts of the sentence — both before and after the semicolon — could stand alone as complete sentences if we removed “however,” which is an independent clause marker here. Also note that a comma follows the coordinating conjunction placed between the two independent clauses.
Fused (“Run-On”) Sentences
❌ No Comma
A fused sentence, also called a “run on” sentence, is an error that occurs when two independent clauses are connected within a single sentence that should instead each stand alone as independent sentences. Run-on sentences are incorrect due to their grammar, not due to sentence length. Here’s an example of a run-on sentence: “She appreciated the party they threw for her she did not appreciate the cake they chose for her.”
There are two options for resolving this error. First, as discussed above, you can use a conjunction like “and,” “but,” and “or” between the independent clauses. That would make the sentence look like this:
She appreciated the party they threw for her, but she did not appreciate the cake they chose for her.
You can also separate the clauses with a semicolon:
She appreciated the party they threw for her; she did not appreciate the cake they chose for her.
Finally, you can separate the clauses with a period (create two separate sentences):
She appreciated the party they threw for her. She did not appreciate the cake they chose for her.
You can use any of these three methods to correct run-on sentences.
Connecting Dependent and Independent Clauses
Example: “The truth is, …”
Dependent clauses that begin a sentence and introduce an independent clause (such as “the truth is” or “on the other hand”) are always followed by a comma. When dependent clauses are followed by an independent clause, a comma separates the two clauses.
For example, note the comma separating the first dependent clause “the truth is” from the following independent clause in the following sentence: “The truth is, she didn’t really want to go to the party”. Notice that the second part of the sentence “she didn’t really want to go to the party” could stand alone; it is an independent clause.
Subordinating conjunctions are words that connect independent and dependent clauses in a sentence. They precede dependent clauses. Depending on the ordering of the dependent and independent clauses — and thus the placement of the subordinate conjunction — you may or may not need to include a comma. Examples of subordinating conjunctions include “whenever,” “after,” “before,” “while,” and “since.” Whether or not you need to use a comma with a subordinating conjunction depends on the context.
Subordinating conjunctions always precede the dependent clause. When the dependent clause comes first, meaning that the subordinate conjunction is placed at the beginning of the sentence, a comma is required to separate the dependent and independent clauses in the sentence.
For example, consider the following sentence: “After I went to the store, I found my dog running around the parking lot.” First, note the placement of the subordinating conjunction at the beginning of the sentence and the comma separating the two clauses. Second, note that without the conjunction (“after”), both clauses could potentially stand alone as complete sentences. However, in this case, with the inclusion of the subordinating conjunction, the dependent clause, “I went to the store” acts as a subordinate (or dependent) clause because it is an extension of the independent clause.
❌ No Comma
Regardless of the placement, the subordinating conjunction modifies the clause such that it changes from an independent to a dependent clause. In other words, with the inclusion of a preceding subordinate conjunction, the clause which carries the conjunction is no longer a complete sentence on its own. However, when the dependent clause is placed second in the sentence, and the subordinating conjunction is placed between the independent and dependent clause, a comma is not needed in the sentence.
Note the difference between the previous sentence construction and the following reconstruction: “I found my dog running around the parking lot after I went to the store.” In this case, the subordinating conjunction acts as a sort of divider between the independent and dependent clause, and a comma is not needed.
Connecting Dependent Clauses
Example: “The truth is …”
❌ No Comma
Contrary to the last rule, when a dependent clause is followed by another dependent clause, connected by a subordinating conjunction, you do not use a comma. Subordinating conjunctions include words like “whenever,” “after,” or “before,” or phrases like “the truth is”.
Note that there is no comma between “the truth is” and the following dependent clause in the following sentence: “The truth is it was difficult.” Neither clause in this sentence — “the truth is” or “it was difficult” — could stand alone as sentences in themselves.
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