Dashes and Hyphens

Prefixes and Compounds
Random Notes on Hyphens


There are three types of dashes:

Em Dash

The em dash, the longest of the three, is used to set off parenthetical matter. Type the em dash with no space on either side.

  • Many of the classes are quite small—10 to 20 students—and students benefit from close contact with the faculty.

The em dash can also be used to introduce a summary:

  • Frequent field trips, audiovisual instruction, a mentor program with industry professionals—these are additional dimensions.

Exception: The em dash is typed with a space on either side on Columbia Business School web pages.

En Dash

The en dash is shorter than the em dash and is used primarily to indicate a range between numbers, substituting for the word “to.” Type the en dash with no space on either side.

  • The assignment can be found on pages 34–36.
  • The conference was held September 21–24.
  • Exception: The en dash is typed with a space on either side on Columbia Business School web pages.

(For more details, please see the Numbers section.)


The Chicago Manual of Style provides an exhaustive guide to the often-confusing hyphen. Some general rules follow.

When compound modifiers (also called phrasal adjectives) such as “high-profile” or “book-length” precede a noun, hyphenation usually lends clarity. With the exception of proper nouns (such as United States) and compounds formed by an adverb ending in “ly” plus an adjective, it is never incorrect to hyphenate adjectival compounds before a noun.

When such compounds follow the noun they modify, hyphenation is usually unnecessary.

Though the trend is generally to close up compound nouns, for example statehouse, boathouse, and townhouse, when in doubt, consult Merriam-Webster’s Collegiate Dictionary (10th edition).  (m-w.com)

The hyphen is also used when a word must be broken at the end of a line and in the formation of compound words like self-reliant and up-to-date.

Prefixes and Compounds

The hyphen’s function, as with all punctuation, is to prevent confusion. Chicago now often recommends closing up words with prefixes and removing the hyphen, only recommending using it to separate two repeated vowels (as in re-educate), to avoid confusion with another word (re-creation/recreation), or to prevent misreading (anti-utopian, co-edition, pro-choice, pro-democracy, pro-life, pro-regent).

For a comprehensive guide to Chicago’s hyphenation policy, consult the Chicago Manual of Style hyphenation table in section 7.59.

*One important instance in which the CBS style guide deviates from Chicago is in the case of “co.” CBS recommends hyphenation with the prefix “co”: co-founder, co-director, co-CEO, co-teacher.

Compounds with well, ill, better, best, little, lesser, and so on are hyphenated when they precede the noun, unless the expression includes another modifier:

  • a little-known fact
  • a well-qualified applicant


  • an exceptionally well qualified applicant

or is not used as a modifier.

  • Two applicants were well qualified.

Compounds like off-campus and part-time should be hyphenated when they precede the word they modify; do not hyphenate when they are adverbial:

  • Students who want off-campus housing should go to room 12.
  • Jobs on campus are usually filled by now.
  • Jack is attending full time this semester, while his mother is a part-time student.
  • On-the-job experience is essential.
  • She acquired most of her experience on the job.
  • They are studying Keynes in depth.


  • an in-depth study of Keynes

In fractions, use a hyphen whether the compound is a noun or an adjective:

  • two-thirds of the students
  • a three-fifths majority

With mixed numbers (integer and fraction), hyphenate the adjective form but not the noun form:

  • He arrived two-and-a-half hours late.
  • The answer was two and a half.

Compounds in which the second element consists of more than one word are hyphenated. When a prefix is added to an open compound, the hyphen becomes an en dash:

  • pre-latency-period
  • non-English-speaking


  • pre–Civil War

When part of a compound is used, a space follows the hyphen: a three- or four-credit course

No Hyphen Is Used...

No hyphen is used between an adverb ending in “ly” and an adjective or participle:

  • rarely seen comet
  • highly complex equation

check in — when used as a verb. Hyphenate when used as a modifier:

  • Please check in at the desk.
  • Meet me at the check-in desk.

A phrase made up of a noun and gerund is typically open when used as a noun, and hyphenated when used as an adjective.

problem solving—when used as a noun. Hyphenate when used as a modifier:

  • The course examines problem solving in organizations.
  • We went mountain climbing


  • The course teaches problem-solving skills for managers.
  • Mountain-climbing course

Exceptions: Chicago recommends certain phrases be hyphenated as both a noun and an adjective, for example, decision-making.

            She is good at decision-making.

Random Notes on Hyphens

Word Breaks and Hyphenation

If a word is broken at the end of a line, a minimum of three letters after the break is required.

Whenever possible, avoid beginning the last line of a paragraph or the first line of a column with a broken word.

Whenever possible, avoid hyphenating at the end of consecutive lines.

When determining whether or not a compound word is hyphenated, refer to Merriam-Webster’s Collegiate Dictionary (10th edition).

Occasionally, our house style departs from Webster’s for the sake of readability. Notable exceptions include words with the prefix “co”:




Other common Columbia Business School exceptions to Merriam Webster Collegiate Dictionary:



Other common words and phrases:

dual-degree program






livestream (as both verb and adjective)

Do not hyphenate percentages:

  • 10 percent discount
  • 12 percent deduction