Subject Index - Punctuation

• colons
• commas
• dashes
• ellipses
• energy efficient
• high-performance computing
• parentheses
• periods
• quotation marks
• semicolons
• slash (solidus)

colons

Colons formally introduce a list or series, a question, or an amplification.

When the colon is followed by a complete sentence, capitalize the first letter of the first word after the colon.

Colons also often separate the parts of a ratio.

However, commas, not colons, usually follow words such as "that is," "namely," and "for example." You don't need a colon after a verb or preposition that precedes or introduces a list ("includes," "to," "with," "between," etc.). Use a colon when a noun (such as "the following") introduces a list in the text.

commas

1. When To Use Commas

Use a comma to separate items in a series, including the next-to-last word in the series.

Use a comma to separate the parts of a compound sentence linked by a coordinating conjunction (such as "and," "but," "or," and "nor") when each part has its own subject and verb (unless they're very short).

Use commas to set off nonessential or nonrestrictive (parenthetical) words, phrases, and clauses from the rest of the sentence. In other words, the commas signal that the information between them is something extra and not essential to the meaning of the sentence.

Use commas to enclose the name of a state when it follows a city and a year when it follows the month and day.

2. When Not To Use Commas

Do not use a comma to separate compound subjects or compound verbs.

Do not use commas to set off words or phrases that are restrictive (i.e., essential to the meaning of a sentence).

See also which and that.

dashes

Use dashes (often called "long dashes" or "em dashes") to enclose and set off parenthetical (nonessential but often illustrative) information in a sentence. Also use dashes to set off a list of items separated by commas. Do not add spaces around the dash.

Use an em dash to signal that an important point is going to be made or that a change in the construction of the sentence follows.

You can usually use commas, colons, and semicolons in place of dashes, but dashes add special emphasis.

Use shorter dashes known as "en dashes" (rather than a hyphen or em dash) to indicate a range or to substitute for the word "to."

In date spans, do not use "from" in conjunction with an en dash (e.g., "from Jan. 16–Feb. 3"). The correct form is "from Jan. 16 to Feb. 3" or "Jan. 16–Feb. 3."

Do not use an en dash (or hyphen) to mean "and"; the word "between" is followed by the word "and" (not "to"): between 25 and 30.

ellipses

When you want to leave out part of text material you are quoting, use ellipsis marks (three dots with a space on each side) to indicate the omission.

If the words before the ellipses form a grammatically correct sentence, put a period at the end of the sentence and follow it by ellipses. In most cases, however, you don't have to use ellipses at the beginning or end of quotes, just within them. When you add a word or words to the quote, to make it clear, enclose the added word or words in brackets to show that it is not part of the original quotation.

When you quote whole paragraphs but omit text between any two of them, center three asterisks, with spaces between them (* * *), between the paragraphs quoted. See also quotation marks.

energy efficient

Hyphenate “energy efficient” only when used as a modifier:

high-performance computing

“High-performance computing” should be hyphenated. The abbreviation HPC can be used to refer to high-performance computing but should not be used to mean high-performance computer. However, the term "supercomputer" may be used in place of high-performance computer.

parentheses

Use parentheses as appropriate for explanatory material in text and as shown in the examples that follow.

1. Parentheses in Equations

In equations, use parentheses, brackets, and braces in this sequence (which may be repeated as needed).

2. Parentheses with Measurements

Use parentheses around English measurements that follow SI (metric) measurements.

3. Parentheses in Citations

When you use parentheses in text, such as for author-date references or for parenthetical (added) information, place a comma after the parentheses rather than before them.

4. Nested Parentheses in Text

In body copy, use parentheses, brackets, and braces in this sequence, which may be repeated as needed: ([{ }]).

periods

Periods are used in some abbreviations (e.g., i.e., a.m., p.m.) and not in others (ac, dc, rpm). Most acronyms do not have periods. When you end a sentence with "etc." (although this is seldom necessary) or another abbreviation that already includes a period, do not add another one.

quotation marks

Use quotation marks for direct quotes and the titles of articles, papers, and book chapters. In print, use "curly" or "fancy" quotation marks; on the web, use "straight" quotation marks. 

Place commas (and periods) inside quotation marks; place semicolons, question marks, dashes, and exclamation points outside quotation marks unless they're part of the quotation.

Use single quotation marks to indicate a quotation within material that is already enclosed in double quotation marks.

When quotations are longer than two or three lines of text, begin them on the next line and indent them on each side (block quotations). You do not need quotation marks around block quotations, and you can use standard double quotation marks for quotes within block quotations. In in-text quotations, place reference numbers, superscripts, and author-date citations outside quotation marks (but before the final punctuation of a sentence). Place them after the final punctuation of the last sentence in a block quotation.

semicolons

Semicolons indicate a stronger or more important break in the flow of words than the break indicated by a comma. Use a semicolon in compound sentences that are NOT linked by a conjunction (such as "and," "but," "or," "nor," and "yet"). Place a semicolon before conjunctive adverbs (such as "however," "hence," "therefore," "nevertheless," and "consequently") in most complex sentences containing two or more clauses. When a sentence contains items in a series, you may use a semicolon between the items if one or more of the items contains commas.

1. Using Semicolons in Compound Sentences without Conjunctions

When clauses in a sentence are closely related in meaning, a semicolon is an appropriate dividing punctuation mark. Note that the words "and," "but," "or," and "nor" do not follow semicolons.

2. Using Semicolons with Conjunctive Adverbs

"Yet" and "so" are usually preceded by commas in a complex sentence. But use a semicolon before such conjunctive adverbs as "then," "however," "thus," "therefore," "hence," "accordingly," "moreover," "nevertheless," "consequently," "besides," "indeed," and "subsequently"; place a comma after the adverb.

Use a semicolon before "i.e." ("that is") and "e.g." ("for example") and a comma after them when a clause (with a subject and verb) follows them; use a comma when a phrase or list follows.

3. Using Semicolons in a Series

When items in a series contain internal punctuation (e.g., commas) or are very long, you can separate them with semicolons. In those cases, a conjunction can follow the last semicolon.

slash (solidus)

The solidus (or slash, slant, shilling mark, or virgule) is a versatile symbol that has mathematical as well as textual functions.

1. Using a Solidus in Fractions

Use a solidus to express a quotient in text when you do not need to use a displayed equation.

Use a solidus in superscript and subscript fractions.

2. Using a Solidus in Text

In text, use a solidus to indicate some junctions, interfaces, and components.

With abbreviated units of measurement, the solidus stands for "per."

But spell out "per" when you spell out the units of measurement.