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Punctuation

The comma is the most frequently used punctuation mark, as well as the one about whose usage writers most often disagree. Examples of common misuses of the comma accompany the following guidelines. The section concludes with advice about editing for unnecessary commas.

1. Use a comma in a compound sentence to separate two independent clauses linked by a coordinating conjunction (and, or, nor, but, so, for, or yet).

2. Use a comma to separate items in a series composed of three or more elements.

The manager of spare parts is responsible for ordering, stocking, and disbursing all spare parts for the entire plant.

Despite the presence of the conjunction and, most technical-communication style manuals require a comma after the second-to-last item. The comma clarifies the separation and prevents misreading.

3. Use a comma to separate introductory words, phrases, and clauses from the main clause of the sentence.

However, we will have to calculate the effect of the wind.

To facilitate trade, the government holds a yearly international conference.

In the following example, the comma actually prevents misreading:

Just as we finished eating, the rats discovered the treadmill.

NOTE: Writers sometimes make errors by omitting commas following introductory words, phrases, or clauses. A comma is optional only if the introductory text is brief and cannot be misread.

4. Use a comma to separate a dependent clause from the main clause.

Although most of the executive council saw nothing wrong with it, the advertising campaign was canceled.

Most tablet computers use green technology, even though it is relatively expensive.

5. Use commas to separate nonrestrictive modifiers (parenthetical clarifications) from the rest of the sentence.

Jones, the temporary chairman, called the meeting to order.

NOTE: Writers sometimes introduce an error by dropping one of the commas around a nonrestrictive modifier.

6. Use a comma to separate interjections and transitional elements from the rest of the sentence.

Yes, I admit that your findings are correct.

Their plans, however, have great potential.

NOTE: Writers sometimes introduce an error by dropping one of the commas around an interjection or a transitional element.

7. Use a comma to separate coordinate adjectives.

The finished product was a sleek, comfortable cruiser.

The heavy, awkward trains are still being used.

The commas in these examples take the place of the conjunction and.

If the adjectives are not coordinate—that is, if one of the adjectives modifies the combined adjective and noun—do not use a comma:

They decided to go to the first general meeting.

8. Use a comma to signal that a word or phrase has been omitted from a sentence because it is implied.

Smithers is in charge of the accounting; Harlen, the data management; Demarest, the publicity.

The commas after Harlen and Demarest show that the phrase is in charge of has not been repeated.

9. Use a comma to separate a proper noun from the rest of the sentence in direct address.

John, have you seen the purchase order from United?

What I’d like to know, Betty, is why we didn’t see this problem coming.

10. Use a comma to introduce most quotations.

He asked, “What time were they expected?”

11. Use a comma to separate cities or towns, states, and countries.

Bethlehem, Pennsylvania, is the home of Lehigh University.

He attended Lehigh University in Bethlehem, Pennsylvania, and the University of California at Berkeley.

Note that a comma precedes and follows Pennsylvania.

12. Use a comma to set off the year in a date.

August 1, 2012, is the anticipated completion date.

If the month separates the date and the year, you do not need to use commas because the numbers are not next to each other:

The anticipated completion date is 1 August 2012.

13. Use a comma to clarify numbers.

12,013,104

NOTE: European practice is to reverse the use of commas and periods in writing numbers: periods separate hundreds and thousands, thousands and millions, and so on, while commas separate whole numbers from decimals.

12. 013, 4

14. Use a comma to separate names from professional or academic titles.

Harold Clayton, PhD

Marion Fewick, CLU

Joyce Carnone, PE

The comma also follows the title in a sentence:

Harold Clayton, PhD, is the featured speaker.

Unnecessary Commas

Writers often introduce errors by using unnecessary commas. Do not insert commas in the following situations:

• Commas are not used to link two independent clauses without a coordinating conjunction (an error known as a “comma splice”).

• Commas are not used to separate the subject from the verb in a sentence.

• Commas are not used to separate the verb from its complement.

• Commas are not used with a restrictive modifier.

• Commas are not used to separate two elements in a compound subject.

Semicolons are used in the following instances:

1. Use a semicolon to separate independent clauses not linked by a coordinating conjunction.

The second edition of the handbook is more up-to-date; however, it is also more expensive.

2. Use a semicolon to separate items in a series that already contains commas.

The members elected three officers: Jack Resnick, president; Carol Wayshum, vice president; Ahmed Jamoogian, recording secretary.

Here the semicolon acts as a “supercomma,” grouping each name with the correct title.

Misuse of Semicolons

Sometimes writers incorrectly use a semicolon when a colon is called for:

Colons are used in the following instances:

1. Use a colon to introduce a word, phrase, or clause that amplifies, illustrates, or explains a general statement.

The project team lacked one crucial member: a project leader.

Here is the client’s request: we are to provide the preliminary proposal by November 13.

We found three substances in excessive quantities: potassium, cyanide, and asbestos.

The week was productive: 14 projects were completed, and another dozen were initiated.

NOTE: The text preceding a colon should be able to stand on its own as a sentence:

2. Use a colon to introduce items in a vertical list if the sense of the introductory text would be incomplete without the list.

We found the following:

3. Use a colon to introduce long or formal quotations.

The president began: “In the last year . . . .”

Misuse of Colons

Writers sometimes incorrectly use a colon to separate a verb from its complement:

Periods are used in the following instances:

1. Use a period at the end of sentences that do not ask questions or express strong emotion.

The lateral stress still needs to be calculated.

2. Use a period after some abbreviations.

U.S.A.

etc.

3. Use a period with decimal fractions.

4.056

$6.75

75.6 percent

The exclamation point is used at the end of a sentence that expresses strong emotion, such as surprise.

The nuclear plant, which was originally expected to cost $1.6 billion, eventually cost more than $8 billion!

In technical documents, which require objectivity and a calm, understated tone, exclamation points are rarely used.

The question mark is used at the end of a sentence that asks a direct question.

What did the commission say about effluents?

NOTE: When a question mark is used within quotation marks, no other end punctuation is required.

She asked, “What did the commission say about effluents?”

Misuse of Question Marks

Do not use a question mark at the end of a sentence that asks an indirect question.

He wanted to know whether the procedure had been approved for use.

To make a dash, use two uninterrupted hyphens (—). Do not add a space before or after the dash. Some word-processing programs turn two hyphens into a dash, but with others, you have to use a special combination of keys to make a dash; there is no dash key on the keyboard.

Dashes are used in the following instances:

1. Use a dash to set off a sudden change in thought or tone.

The committee found—can you believe this?—that the company bore full responsibility for the accident.

That’s what she said—if I remember correctly.

2. Use a dash to emphasize a parenthetical element.

The managers’ reports—all 10 of them—recommend production cutbacks for the coming year.

Arlene Kregman—the first woman elected to the board of directors—is the next scheduled speaker.

3. Use a dash to set off an introductory series from its explanation.

Wet suits, weight belts, tanks—everything will have to be shipped in.

NOTE: When a series follows the general statement, a colon replaces the dash.

Everything will have to be shipped in: wet suits, weight belts, and tanks.

Misuse of dashes

Sometimes writers incorrectly use a dash as a substitute for other punctuation marks:

Parentheses are used in the following instances:

1. Use parentheses to set off incidental information.

Please call me (x3104) when you get the information.

Galileo (1564–1642) is often considered the father of modern astronomy.

The cure rate for lung cancer almost doubled in thirty years (Capron, 2012).

2. Use parentheses to enclose numbers and letters that label items listed in a sentence.

To transfer a call within the office, (1) place the party on HOLD, (2) press TRANSFER, (3) press the extension number, and (4) hang up.

Use both a left and a right parenthesis—not just a right parenthesis—in this situation.

Misuse of Parentheses

Apostrophes are used in the following instances:

1. Use an apostrophe to indicate possession.

the manager’s goals  the employees’ credit union

the workers’ lounge  Charles’s T square

For joint possession, add an apostrophe and an s only to the last noun or proper noun:

Watson and Crick’s discovery

For separate possession, add an apostrophe and an s to each of the nouns or pronouns:

Newton’s and Galileo’s theories

NOTE : Do not add an apostrophe or an s to possessive pronouns: his, hers, its, ours, yours, theirs.

2. Use an apostrophe to indicate possession when a noun modifies a gerund.

We were all looking forward to Bill’s joining the company.

The gerund joining is modified by the proper noun Bill.

3. Use an apostrophe to form contractions.

I’ve shouldn’t

can’t it’s

The apostrophe usually indicates an omitted letter or letters:

can(no)t = can’t

it (i)s = it’s

NOTE: Some organizations discourage the use of contractions. Find out what the policy of your organization is.

4. Use an apostrophe to indicate special plurals.

three 9’s

two different JCL’s

the why’s and how’s of the problem

NOTE: For plurals of numbers and abbreviations, some style guides omit the apostrophe: 9s, JCLs. Because usage varies considerably, check with your organization.

Misuse of Apostrophes

Writers sometimes incorrectly use the contraction it’s in place of the possessive pronoun its.

Quotation marks are used in the following instances:

1. Use quotation marks to indicate titles of short works, such as articles, essays, or chapters.

Smith’s essay “Solar Heating Alternatives” was short but informative.

2. Use quotation marks to call attention to a word or phrase used in an unusual way or in an unusual context.

A proposal is “wired” if the sponsoring agency has already decided who will be granted the contract.

NOTE: Do not use quotation marks to excuse poor word choice:

3. Use quotation marks to indicate a direct quotation.

“In the future,” he said, “check with me before authorizing any large purchases.”

As Breyer wrote, “Morale is productivity.”

NOTE: Quotation marks are not used with indirect quotations:

Also note that quotation marks are not used with quotations that are longer than four lines; instead, set the quotation in block format. In a word-processed manuscript, a block quotation is usually introduced by a complete sentence followed by a colon and indented one-half inch from the left-hand margin.

Different style manuals recommend variations on the basic rules; the following example illustrates APA style.

McFarland (2011) writes:

The extent to which organisms adapt to their environment is still being charted. Many animals, we have recently learned, respond to a dry winter with an automatic birth control chemical that limits the number of young to be born that spring. This prevents mass starvation among the species in that locale. (p. 49)

Hollins (2012) concurs. She writes, “Biological adaptation will be a major research area during the next decade” (p. 2).

Using Quotation Marks with Other Punctuation

• If the sentence contains a tag—a phrase identifying the speaker or writer—a comma separates it from the quotation:

Wilson replied, “I’ll try to fly out there tomorrow.”

“I’ll try to fly out there tomorrow,” Wilson replied.

Informal and brief quotations require no punctuation before a quotation mark:

She asked herself “Why?” several times a day.

• In the United States (unlike most other nations where English is spoken), commas and periods following quotations are placed within the quotation marks:

The project engineer reported, “A new factor has been added.”

“A new factor has been added,” the project engineer reported.

• Question marks, dashes, and exclamation points are placed inside quotation marks when they are part of the quoted material:

He asked, “Did the shipment come in yet?”

• When question marks, dashes, and exclamation points apply to the whole sentence, they are placed outside the quotation marks:

Did he say, “This is the limit”?

• When a punctuation mark appears inside a quotation mark at the end of a sentence, do not add another punctuation mark:

Ellipses (three spaced periods) indicate the omission of material from a direct quotation.

Insert an ellipsis after a period if you are omitting entire sentences that follow:

Larkin refers to the project as “an attempt . . . to clarify the issue of compulsory arbitration. . . . We do not foresee an end to the legal wrangling . . . but perhaps the report can serve as a definition of the areas of contention.”

The writer has omitted words from the source after attempt and after wrangling. After arbitration, the writer has inserted an ellipsis after a period to indicate that a sentence has been omitted.

NOTE: If the author’s original statement has ellipses, MLA style recommends that you insert brackets around an ellipsis that you introduce in a quotation.

Sexton thinks “reuse adoption offers . . . the promise to improve business [. . .] worldwide.”

Square brackets are used in the following instances:

1. Use square brackets around words added to a quotation.

As noted in the minutes of the meeting, “He [Pearson] spoke out against the proposal.”

A better approach would be to shorten the quotation:

The minutes of the meeting note that Pearson “spoke out against the proposal.”

2. Use square brackets to indicate parenthetical information within parentheses.

(For further information, see Charles Houghton’s Civil Engineering Today [1997].)