Student's guide to writing college papers, Fourth edition - Kate L. Turabian 2010
Independent clauses
Punctuation
Style
A compound sentence is composed of two or more independent clauses that could be punctuated as complete sentences. You must separate the independent clauses within a sentence in one of eight ways. The following list groups them into the most common cases, less common cases, and cases for special effects. In all cases, you could end each clause with a period or question mark and make one compound sentence into two or more complete sentences.
22.2.1 Summary
You have eight ways to punctuate the independent clauses in a compound sentence:
1. Comma + Coordinate Conjunction
2. Semicolon
3. Semicolon + Coordinate Conjunction
4. Coordinate Conjunction (alone)
5. Comma (alone)—Caution!
6. Colon
7. Dash
8. Parentheses
22.2.2 Eight Ways to Punctuate Compound Sentences Three common forms:
1. Comma + Coordinate Conjunction (and, but, or, nor, for, so, yet)
This is the most common form. If the individual clauses are long or include internal punctuation, use a semicolon instead (see #3, below).
Students around the world want to learn English, and many young Americans are eager to teach them.
Three or more clauses. In this case, put a comma after each clause (including the one before the conjunction) and a conjunction before the last clause.
The committee designed the questionnaire, the field-workers collected responses, and the statisticians analyzed the results.
2. Semicolon
Students around the world want to learn English; many young Americans are eager to teach them.
Watch out for words that connect sentences but are not conjunctions: however, thus, therefore, hence, then, indeed, accordingly, besides, and so on. Because these are not conjunctions, you cannot use them with a comma in a compound sentence. Use a semicolon instead.
Productivity per capita in U.S. industry is much greater than that in China; however, China has an increasingly well-educated young labor force.
3. Semicolon + Coordinate Conjunction
This form is generally reserved for sentences with complex clauses, especially those with internal punctuation. If the clauses are short, use a comma instead (see #1 above).
Although productivity per capita in U.S. industry is much greater than that in China, China has an increasingly well-educated young labor force; but the crucial point is that knowledge—which is transferable between peoples—has become the most important world economic resource.
Three or more complex clauses. In this case, put a semicolon after each clause (including the one before the conjunction) and a conjunction before the last clause.
The committee designed the questionnaire, which was short but still took more than a month to be completed; the field-workers, who were forced to wait for the committee to finish its work, collected responses; and the statisticians analyzed the results, though not until several weeks later.
Two less common forms:
4. Coordinate Conjunction (alone)
This form is reserved for sentences with two short, simple clauses. Do not use it if either clause has internal punctuation.
The senator arrived at noon and the president left at once.
The senator, who was late, arrived at noon, and the president left at once.
5. Comma (alone)—Caution!
This form is used by many of the best writers when they want to emphasize the connection between two short independent clauses. But many teachers regard this construction as an error (called a comma splice). So avoid it unless you know your readers will accept it.
The senator arrived, the president left.
Three forms for special effects:
6. Colon
A colon suggests that the second clause follows closely from the first. Readers take it as shorthand for therefore, to illustrate, for example, that is, let me expand on what I just said, and so on. The second clause generally does not begin with a capital letter, but it can. Good writers rarely include a coordinating conjunction after a colon.
Dance is not widely supported: no company operates at a profit, and there are few outside major cities.
Only one question remains: What if we lose money?
Only one choice remained: He must confront his enemy.
A colon can also introduce a list of sentences.
Sally was faced with few good choices: She could risk revealing what she learned. Or she could let her best friend pay the price for something she did not do. Or was there a third way?
7. Dash
A dash can be used to signal the same relationships as a colon. It suggests a more informal style, and generally seems to readers like a longer pause. Writers often use a coordinating conjunction or another introducer in the clause after the dash.
NASA's moon program captured America's imagination—we were filled with pride.
Writing well may be hard—but it's worth the effort.
A perfect lawn requires constant diligence—after all, weeds are always poised to invade.
8. Parentheses
You can use parentheses in place of a colon or a dash if the second clause is short and serves as an explanation, illustration, or afterthought. Put the period outside the last parenthesis.
The first moon landing captivated America (the TV ratings were the highest ever).
Writing well may be hard (but it's worth the effort).
A perfect lawn requires constant diligence (after all, weeds are always poised to invade).