Punctuation

In General

Use a single space after punctuation at the end of a sentence and after colons and semicolons.

Apostrophes

When indicating the possessive for names, use an apostrophe followed by an s unless the name ends in s.

  • Kansas’ team
  • Jones’ theorem
  • Marx’s ideas

With a few exceptions, the possessive of a singular common noun is formed with the addition of an apostrophe and s, and the possessive of a plural common noun by the addition of an apostrophe only.

  • The horse’s mouth
  • The puppies’ tails
  • The children’s desk

Do not use an apostrophe to indicate plurals, including the plurals of acronyms and abbreviations, unless confusion would result without the apostrophe (as in the first two examples).

  • There are five s’s in that word.
  • She received straight A's.
  • There are five 5s in that number.
  • There were five PhDs in last year’s class.
  • Five NGOs were represented at the conference.

Apostrophes are required for bachelor’s degreeԻmaster’s degree.

The following organizations commonly contain errors in apostrophe use. These are correctly punctuated. Note the absence or presence of apostrophes.

  • Presidents Leadership Class
  • President’s Teaching Scholars

Colons

Use a colon to introduce a series or a list, especially a list preceded by as followsǰthe following.

Use a colon to introduce an explanatory phrase or sentence. Capitalize the first word after a colon only if it is a proper noun or the start of a complete sentence.

  • Conference participants should bring the following items: laptop computer, notebook and business cards.
  • The implication of the chancellor's challenge was clear: Students must not be overburdened by bureaucracy if they are to enjoy a fulfilling educational experience.

Commas

In a Series

Do not put a comma before the conjunction and the final element in a simple series. Do use a comma before the final conjunction in a complex series of phrases or when needed to avoid ambiguity.

  • The flag is red, white and blue
  • Bachelor’s degrees are offered in biochemistry, ecology and evolutionary biology, and chemistry.

In Complex and Compound Sentences

Use a comma before a conjunction that introduces an independent clause. Note that you do not need a comma before every and,but,becauseԻor. If what follows the conjunction is not a complete clause, you don’t need a comma (as in the second example).

  • The orchestra is giving a concert at Macky Auditorium on Friday night, and the Takács Quartet is performing in Grusin Music Hall on Monday night.
  • I like to go to football games and watch the marching band.

With Appositives

Use commas with appositives that are nonrestrictive (not essential to the meaning of the sentence). Do not use a comma with appositives that are restrictive (essential to the noun it belongs to).

  • The former administrator, Chris Jones, implemented the program in 2005.
  • Professor Greene teaches the course Scientific Writing in Integrative Physiology.

With Dates

No comma is needed between a month and a year. Do use a comma before and after the year if month, date and year are used.

  • The deadline is April 1, 2025, for on-campus applicants and May 1, 2025, for off-campus applicants. A hiring decision will be made in May 2025.

With Introductory Phrases

Use a comma to separate an introductory clause or phrase from the main clause. The comma may be omitted after short introductory phrases if no ambiguity would result.

  • When classes resumed after the winter break, students lined up at the book store.
  • When it’s windy the kinetic sculpture near the Integrated Teaching and Learning Laboratory is fascinating to watch.

With Nonrestrictive and Parenthetical phrases

Use commas to set off nonrestrictive and parenthetical phrases.

  • The Conference on World Affairs, which is free and open to the public, is presented every April.
  • My alternate route, the one I take when I have time, follows Boulder Creek.

With Names of States and Countries

Names of states (or countries) are enclosed in commas when they are preceded by a city (or state).

  • The conference will be held in Eugene, Oregon, but the planning meeting will be held in Frankfurt, Germany. The guest speaker is from Washington, D.C.

Dashes

Observe the distinction between hyphens, en dashes and em dashes (“regular” dashes). None should be set off with spaces.

En Dashes

Use en dashes between inclusive numbers, and date and time ranges.

  • You’ll find the examples on pages 223–26 of your text.
  • She was hired in the 2023–24 academic year.
  • We meet 2–4 p.m. in the UMC. 

Em Dashes

Em dashes are used to denote a sudden break in thought that causes an abrupt change in sentence structure. Do not overuse em dashes; they can interfere with the continuity of the look and the readability of your publication and sometimes cause display issues online, especially in email.

  • Each April participants representing a wide range of backgrounds gather in Boulder—a beautiful college town at the foot of the Rockies—for the Conference on World Affairs.

Ellipses

Use ellipses to indicate that material has been omitted from the middle of a quotation. Do not use ellipses at the beginning or end of a quotation even if you start or stop in the middle of the quoted sentence. Ellipses are created with three period characters, with one space on either side of each character: ( . . . ) not (...)

  • Frank’s speech began with a request that audience members “leave all video cameras, tape recorders and still cameras with the staff . . . at the entrance.”

When the omitted material includes a period, use a period plus ellipses:

  • The Norlin Charge to the graduates reads, “You are now certified to the world at large as alumni of the university. . . . With hope and faith, I welcome you into the fellowship.”

Hyphens

Most questions about whether to hyphenate can be readily answered by consulting your dictionary (CU Boulder uses Merriam-Webster). In general, the fewer hyphens the better. Compound adjectives that precede nouns should be hyphenated when necessary to avoid ambiguity.

  • The top-seeded player won the tournament.
  • She had a part-time job, but her roommate worked full time.

Do not use a hyphen in a compound that begins with an adverb ending in ly:

  • This is a highly regarded program.

Periods

Use periods when you come to the end of a declarative sentence and with some abbreviations (do not add an extra period if the abbreviation ends the sentence).

Quotation Marks

Commas and periods always go inside quotation marks. Colons and semicolons always go outside quotation marks. With question marks and exclamation points, it depends: If the punctuation is part of the quotation, put it inside the quotation marks; if it’s not part of the quotation, put it outside.

Use quotation marks to indicate: the exact words that someone spoke or published, the first time you refer to a nickname and when introducing an unfamiliar term.

Semicolons

Use semicolons to indicate a greater separation of thought and information than a comma can convey or to separate elements.

  • CU officials at the meeting included Todd Saliman, president; Justin Schwartz, Boulder campus chancellor; and Katy Kotlarczyk, vice chancellor for advancement.