Students are often told to use a comma to signal a pause. Comma equals pause is a good rule of thumb, but it neglects the basic principle underlying most of the punctuation choices writers make: commas, periods, semicolons, colons, and dashes are inserted according to the structure, or grammar, of the sentence. More specifically, the rules that govern punctuation are determined by the rules that govern coordination and subordination.

Standard mistakes involving coordination: run-on sentences and comma splices

Run-ons and comma splices, two of the most common mistakes involving coordination,^[1] happen when independent clauses (or sentences) ^[2] are joined without the proper punctuation.

Take, for example, the following two sentences:

SENTENCE 1: One of Gorbachev’s grandfathers was briefly deported to Siberia in the 1930s.

SENTENCE 2: The other was arrested during the Great Terror.

A run-on sentence joins sentences without any punctuation:

One of Gorbachev’s grandfathers was briefly deported to Siberia in the 1930s the other was arrested during the Great Terror.

A comma splice joins sentences using a comma:

One of Gorbachev’s grandfathers was briefly deported to Siberia in the 1930s, the other was arrested during the Great Terror.

There are three ways to correctly join sentences without creating run-on sentences or comma splices:

SEMICOLON OR DASH:^[3] One of Gorbachev’s grandfathers was briefly deported to Siberia in the 1930s; the other was arrested during the Great Terror.

One of Gorbachev’s grandfathers was briefly deported to Siberia in the 1930s—the other was arrested during the Great Terror.

COMMA AND COORDINATING CONJUNCTION: One of Gorbachev’s grandfathers was briefly deported to Siberia in the 1930s, and the other was arrested during the Great Terror.

SEMICOLON, TRANSITIONAL WORD, COMMA: One of Gorbachev’s grandfathers was briefly deported to Siberia in the 1930s; moreover, the other was arrested during the Great Terror.

 

[1] The other common mistake involving coordination is faulty parallelism, covered in Chapter 13.

[2] We covered independent and subordinate (or dependent) clauses in Chapter 2. An independent clause has a subject and a verb, and can stand on its own as a complete sentence.

[3] Colons may also be used to join sentences when the second sentence explains or illustrates the first. E.g.: “Devalued currency made raw materials and imports more expensive: non-fuel commodities went up by 70 percent and food by 100 percent.”