Punctuation

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, Commas

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).

    INCORRECT The mixture was prepared from the two premixes and the remaining ingredients were then combined.
    CORRECT The mixture was prepared from the two premixes, and the remaining ingredients were then combined.
  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.

    CONFUSING The report will be distributed to Operations, Research and Development and Accounting.
    CLEAR The report will be distributed to Operations, Research and Development, and Accounting.
  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.

    CORRECT First, let’s take care of the introductions.
    CORRECT First let’s take care of the introductions.
    INCORRECT As the researchers sat down to eat the laboratory rats awakened.
    CORRECT As the researchers sat down to eat, the laboratory rats awakened.

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  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.

    For more about restrictive and nonrestrictive modifiers, see “Structuring Effective Sentences” in Ch. 6.

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

    INCORRECT The data line, which was installed two weeks ago had to be disconnected.
    CORRECT The data line, which was installed two weeks ago, had to be disconnected.
  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.

    INCORRECT Our new statistician, however used to work for Konaire, Inc.
    CORRECT Our new statistician, however, used to work for Konaire, Inc.
  7. Use a comma to separate coordinate adjectives.

    For more about coordinate adjectives, see “Writing Grammatically Correct Sentences” in Ch. 6.

    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.

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    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, 2016, 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 2016.

  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.

MISUSE OF COMMAS

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

For more about comma splices, see “Writing Grammatically Correct Sentences” in Ch. 6.

INCORRECT All the motors were cleaned and dried after the water had entered, had they not been, additional damage would have occurred.
CORRECT All the motors were cleaned and dried after the water had entered; had they not been, additional damage would have occurred.
CORRECT All the motors were cleaned and dried after the water had entered. Had they not been, additional damage would have occurred.

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INCORRECT Another of the many possibilities, is to use a “first in, first out” sequence.
CORRECT Another of the many possibilities is to use a “first in, first out” sequence.
INCORRECT Recent studies, and reports by other firms confirm our experience.
CORRECT Recent studies and reports by other firms confirm our experience.

; SEMICOLONS

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.

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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:

INCORRECT We still need one ingredient; luck.
CORRECT We still need one ingredient: luck.

: COLONS

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:

    INCORRECT We found: potassium, cyanide, and asbestos.
    CORRECT We found the following: potassium, cyanide, and asbestos.
    CORRECT We found potassium, cyanide, and asbestos.
  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:

    • potassium

    • cyanide

    • asbestos

  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:

INCORRECT The tools we need are: a plane, a level, and a T square.
CORRECT The tools we need are a plane, a level, and a T square.
CORRECT We need three tools: a plane, a level, and a T square.

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. PERIODS

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

For more about abbreviations, see page 500.

! EXCLAMATION POINTS

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.

? QUESTION MARKS

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.

DASHES

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:

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  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:

INCORRECT The regulations—which were issued yesterday—had been anticipated for months.
There would be no reason to emphasize this parenthetical element.
CORRECT The regulations, which were issued yesterday, had been anticipated for months.
INCORRECT Many candidates applied—however, only one was chosen.
CORRECT Many candidates applied; however, only one was chosen.

( ) PARENTHESES

Parentheses are used in the following instances:

  1. Use parentheses to set off incidental information.

    Please call me (×3104) 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, 2016).

  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.

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MISUSE OF PARENTHESES

Read more about square brackets.

Sometimes writers incorrectly use parentheses instead of brackets to enclose their insertion within a quotation:

INCORRECT He said, “The new manager (Farnham) is due in next week.”
CORRECT He said, “The new manager [Farnham] is due in next week.”

APOSTROPHES

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

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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.

INCORRECT The company’s management does not believe that the problem is it’s responsibility.
CORRECT The company’s management does not believe that the problem is its responsibility.

“ ” QUOTATION MARKS

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:

    INCORRECT The new director has been a real “pain.”
  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:

    INCORRECT He said that “third-quarter profits will be up.”
    CORRECT He said that third-quarter profits will be up.
    CORRECT He said, “Third-quarter profits will be up.”

    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)

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

For more about quoting sources, see “Note Taking” in Appendix, Part A.

USING QUOTATION MARKS WITH OTHER PUNCTUATION

. . . ELLIPSES

Ellipses (three spaced periods) indicate the omission of material from a direct quotation. (Word processors have a special character for ellipses.)

SOURCE My team will need three extra months for market research and quality-assurance testing to successfully complete the job.
QUOTE She responded, “My team will need three extra months . . . to successfully complete the job.”

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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

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].)