Comma Rule No. 1—Joining Independent Clauses
Can Each Part of the Sentence Stand Alone?
Oct 15, 2009
The comma, the most used piece of punctuation in the English language, is also the most misunderstood. This is because the comma is used in so many different ways although its basic purpose remains the same: to clarify the elements of a sentence.
Comma usage requires the writer to carefully consider why each comma is necessary. This is why the advice often given to students--place a comma wherever you would pause in a sentence while speaking--falls short. For example, in a lengthy sentence such as the following:
- Learning the proper way to use commas can only enhance a student’s skills in writing and reading.
Some speakers might pause after the word “commas.” Others may pause after “skills” or "writing." In truth, no commas are needed in the sentence.
Learning a few simple rules can help all writers communicate more effectively and avoid embarrassing mistakes. One of the most common rules governs the usage of commas while joining independent clauses.
Independent Clauses
So, what exactly is an independent clause? A clause is an arrangement of words with a subject and a verb. Clauses that can stand alone as complete sentences are considered independent clauses. Thus, a two-word sentence such as "Billy cried" needs nothing more to complete it, as it has both a subject (Billy) and a verb (cried).
Of course, clauses may and usually do have more than two words: "John went to the store" is another independent clause.
A dependent clause, by contrast, has both a subject and a verb, yet it needs something else to complete it. For example, if the word after is placed in front of “John went to the store,” another clause—an independent clause—is needed to complete the thought:
- After John went to the store, he made dinner.
The phrase “he made dinner” can stand on its own, even if the reader doesn’t know who “he” is or what he did before he made dinner. It is, therefore, an independent clause.
Joining Independent Clauses
The rule: Use a comma to join two independent clauses:
- John went to the store, and he bought milk.
Notice the coordinating conjuction—the word and. A coordinating conjunction is a word that connects two parts of a sentence that have equal value. Other common coordinating conjunctions are so, but, for, or, nor, and yet.
Inexperienced writers often write such sentences this way:
- John went the the store, he bought milk.
This, however, creates a type of error known as a comma splice, where two sentences are joined together improperly with a comma. The problem here is that the comma suggests that one part of the sentence depends on the other other, when, in fact, neither does. (Note also that other methods, such as a period or semi-colon in place of the comma, would also correct the sentence.)
When to Leave the Comma Out
Suppose the writer wants to shorten the sentence:
- John went to the store and bought milk.
In this case, the comma is removed because the phrase “bought milk” cannot stand on its own.
For more information on commas, see Comma Rule Nos. 2, 3, and 4.
Test Yourself
Are commas needed in the following sentences? (The answer appears at the end of the article.)
a. John went to the store and Mary made dinner.
b. Abraham Lincoln was the sixteenth president and was assassinated.
c. George Washington was the first president but he never lived in the White House.
d. John Adams came in second in the election so he became the first vice president.
e. Adams later became president but served only one term.
Use a comma to separate two independent clauses in a sentence, but make sure that both parts of the sentence are, in fact, independent clauses. (Answer: commas are needed in sentences a, c, and d.)
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