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Writer's Handbook

Comma Splices (Run-Ons) and Fused Sentences

The term comma splice refers to the use of just a comma to join two independent clauses (that is, two groups of words that could each stand alone as a complete sentence). Here's an example:

  • He didn't study at all for the test, he got a B+ on it.

"He didn't study at all for the test" could stand alone as a complete sentence, and so could "he got a B+ on it." The comma "splices" together two groups of words which should be separated by something more emphatic than just a comma--thus the term "comma splice."

Some English teachers (and some other people) use the term "run-on sentence" rather than "comma splice" to describe passages such as "He didn't study at all for the test, he got a B+ on it," because the sentence "runs on" rather than stopping after "test." But on this web page we'll employ the more commonly used term: comma splice.

The sentence above could be fixed any of several ways:

  1. By adding a conjunction such as and, but, or, etc., with a comma, before the conjunction.
    • He didn't study at all for the test, but he got a B+ on it.
  2. By replacing the comma with a period.
    • He didn't study at all for the test. He still got a B+ on it.
  3. By replacing the comma with a semicolon.
    • He didn't study at all for the test; he got a B+ on it anyway.
  4. By replacing the comma with a semicolon and also adding a conjunctive adverb such as however, therefore, or nevertheless.
    • He didn't study at all for the test; nevertheless, he got a B+ on it.
  5. By changing the sentence structure, for example by beginning the sentence differently.
    • Although he didn't study at all for the test, he still got a B+ on it.

Probably the most common source of comma splices in college students' papers is difficulty handling conjunctive adverbs in general and the word however in particular. The basic rule is this: if a conjunctive adverb joins two independent clauses (in other words, if the words before the conjunctive adverb could stand alone as a complete sentence, and so could the words after the conjunctive adverb), then there should be either a semicolon or a period (either one is correct) before the conjunctive adverb, and a comma after it. Here are examples:

  • Some of us wanted to go to an expensive French restaurant; however, we ended up just going out for barbecue.
  • Some of us wanted to go to an expensive French restaurant. However, we ended up just going out for barbecue.

A comma before "however" in the above examples, rather than a semicolon or period, would create a comma splice.

If, however, the conjunctive adverb comes in the middle of a single independent clause (in other words, if the words on one side or the other couldn't stand alone as a complete sentence), then there should be commas before and after the conjunctive adverb. The sentence you just read is an example:

  • If, however, the conjunctive adverb comes in the middle of a single independent clause, then there should be commas before and after the conjunctive adverb.

In the above sentence, it would be incorrect to put a semicolon or period before the "however."

Another frequent source of comma splices is the word then when that word joins two independent clauses. For example, the following is a comma splice:

  • Mary won her first six matches in a row, then she lost the next five in a row.

The above sentence could be fixed by putting a period or semicolon before then, but simpler solutions would be either to add a conjunction before then (to make the sentence into a compound sentence) or to eliminate the word she immediately after then (so that then is no longer joining two independent clauses):

  • Mary won her first six matches in a row, but then she lost the next five in a row.
  • Mary won her first six matches in a row but then lost the next five in a row.

Either of these revisions is grammatically correct.

The term fused sentences refers to joining two complete sentences without any punctuation at all. In other words, fused sentences are a comma splice without the comma. Here's the example from earlier, reworked as fused sentences:

  • He didn't study at all for the test he got a B+ on it.

Fused sentences are much rarer than comma splices in college students' writing, and most teachers consider fused sentences to be much more serious types of errors. The ways of fixing fused sentences, however, are essentially the same as those for fixing comma splices: adding a conjunction with a comma before it, or adding a period or semicolon, or rewording the sentence.