Phrases, Clauses, and Sentences
Common Sentence Errors
One of the most common mistakes with independent clauses is joining them without the proper punctuation. This error is called a run-on sentence or comma splice. An independent clause standing alone should end in a period, question mark, or exclamation point.
Joining independent clauses
If you want to join independent clauses, however, you should use a semicolon or one of the seven coordinating conjunctions between them. A comma should precede the coordinating conjunction, but a comma without a conjunction is not sufficient.
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He drove off in the Mercedes, Erica watched him go. (no)
This is a run-on sentence, or comma splice. A comma alone cannot join independent clauses.
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He drove off in the Mercedes. Erica watched him go. (yes)
Here, the independent clauses are separate sentences. Each ends correctly with a period.
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He drove off in the Mercedes; Erica watched him go. (yes)
The two independent clauses are correctly joined with a semicolon.
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He drove off in the Mercedes, and Erica watched him go. (yes)
The two independent clauses are correctly joined with a coordinating conjunction (and) preceded by a comma.
Run-ons with conjunctive (sentence) adverbs
Watch out for another kind of run-on sentence. Some words look like coordinating conjunctions but aren't. These words cannot be used to join independent clauses with a comma. Remember that the only time you can join independent clauses with a comma and not be guilty of a run-on sentence is when one of the seven coordinating conjunctions (and, but, for, nor, or, so, yet) follows the comma.
The impostors—words that look suspiciously like coordinating conjunctions but are actually adverbs—we called conjunctive adverbs or sentence adverbs. The use of a comma to join a clause beginning with one of these words is widespread in business and official writing, but no matter how common the practice, it still creates a run-on, and most teachers and editors won't accept it. Table
1 shows a few of the words to watch out for.
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Some transitional phrases pose the same problem—for example, as a result, even so, for example, in other words, on the contrary. If you keep in mind the rule that independent clauses can be joined with a comma only when the comma is followed by one of the seven coordinating conjunctions, you should be able to avoid these tricky run-ons.
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Scientists were convinced by the evidence; however, the Food and Drug Administration was slow to respond.
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not Scientists were convinced by the evidence, however, the Food and Drug Administration was slow to respond.
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The hurricane damaged the arena. Nevertheless, the game was played on schedule.
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not The hurricane damaged the arena, nevertheless, the game was played on schedule.
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Folic acid appears to exert a protective effect. For example, one study showed that it cut the rate of neural tube defects by two-thirds.
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not Folic acid appears to exert a protective effect, for example, one study showed that it cut the rate of neural tube defects by two-thirds.
Acceptable run-ons
Run-on sentences such as the ones described above are basic errors. Occasionally, however, joining independent clauses with only a comma may be acceptable—for example, when the clauses are very short and have the same form, when the tone is easy and conversational, or when you feel that the rhythm of your sentence calls for it.
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Live by the sword, die by the sword.
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They smiled, they touched, they kissed.
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I hardly recognized her, she was so thin. (A because is understood here.)
But be very careful about creating an intentional run-on. Have a good reason to do so; don't break such a basic sentence rule lightly.
