Student writers often confuse the hyphen and dash. A hyphen is a short line (-) used to join words; it occurs on most keyboards as an actual key. A dash is a longer line (—) used to set off or separate phrases; it does NOT occur on most keyboards as an actual key. A dash can be automatically generated in Microsoft Word, however, by typing two hyphens between words like this: A dash--generated with two hyphens--is a useful writing tool. (After you use “space bar” to move away from the word following the double hyphens, MS Word will automatically change it into a dash.) If you are using a word processing program that does not automatically convert double hyphens to a dash, then it is acceptable to use the two hyphens in place of the dash.
Now that we’re clear on that point, let’s focus on the hyphen. If you are looking for infallible rules for when to use the hyphen, you are out of luck: its use is constantly evolving! The following uses, however, are generally agreed upon, with a few exceptions here and there.
1. To join two or more words serving as a single adjective before a noun (a.k.a., a compound modifier)
Asbestos is a well-known carcinogen.
Look online for up-to-date images of the oil spill.
Predictions from large-scale global climate models can be a valuable resource for city planners.
Note: When the adjective follows the noun, the words are NOT hyphenated.
The carcinogenic properties of asbestos are well known.
The images of the oil spill are up to date.
Predictions from global climate model can be a valuable resource for city planners in spite of the models' large scale.
[In these cases, "well known," “up to date,” and "large scale" follow the nouns they're modifying, so they are not hyphenated.]
2. To join compound numbers under one hundred and fractions
Examples: thirty-five, fifty-two or five-eighths
Hyphens are usually not used with numbers greater than one hundred, unless they occur within the greater number:
Example: one hundred twenty-one
Note: While hyphens are used to write out numbers when required, it is acceptable in most cases to write numbers that are greater than ten numerically (e.g., 12 instead of twelve).
3. To avoid confusion or awkward combinations of letters
re-sign a purchase order (vs. resign from a job)
re-creation of the compound (vs. parks and recreation)
re-enter the facility (vs. “reenter”)
4. To avoid ambiguities
a little-used car vs. a little used-car
third-world environmental degradation vs. third world environmental degradation
5. To join certain prefixes and suffixes to words.
Examples: Use a hyphen with the prefixes ex-, self-, all-, half-, semi-, quasi-, non-, post-, and neo-.
Example: Use a hyphen with the suffix –elect.
Example: Use a hyphen between a prefix and a capitalized word or acronym.
Example: Use a hyphen and with figures or letters.
Note: In all of the above cases, there are NO SPACES on either side of the hyphen.
6. To split words between lines when using a justified text format.
Whenever possible, keep a word that isn’t hyphenated together, but when it does get broken at the end of a line, make the break only between syllables or where a word is already hyphenated.
Examples: en-vi-ron-ment-al-ist, warm-ing, plan-ning, or mass-produced
Note: Never put a single letter at the beginning or end of a line and never put two-letter suffixes at the beginning of a new line.
extremely (Do not separate to leave “ly” beginning a new line.)
avail-a-ble (Separate only on either side of the a; do not leave the initial “a” at the end of a line.)
Suspended hyphens (a.k.a., “dangling” or “hanging” hyphens) are used in series of related compound words separated by “and” “or” or “to.” In these cases, the hyphen acts as a kind of place holder.
The first- and second-year MESM students are brilliant.
The proposed logging site is full of two- and three-hundred-year-old trees.
1. The hyphen as a separator
The hyphen’s main purpose is to join words, but people still sometimes use it INCORRECTLY as a “separator,” frequently in place of a comma.
Once you’ve run the model-add it to your GIS display. (Incorrect)
Once you’ve run the model, add it to your GIS display. (Correct)
Other “separators” that are more appropriate include the period (hyphens can be an indicator of run-on sentences), the colon, the semicolon, or the dash (visit the Communication Center’s blog posts for more information on each of these “separators.”)
2. The hyphen as a delimiter.
Another common mis-use of the hyphen is to delineate internal or parenthetical phrases.
Incorrect Example: Black carbon-unlike greenhouse gases-stays in the atmosphere only for a few weeks.
This incorrectly hyphenated sentence is confusing, because people will read it as
Black carbon-unlike . . .
greenhouse gases-stays . . .
in the atmosphere only for a few weeks.
…when what the writer really meant was
Black carbon . . .
unlike greenhouse gases . . .
stays in the atmosphere only for a few weeks.
This sentence should be correctly written with dashes as follows:
Black carbon—unlike greenhouse gases—stays in the atmosphere only for a few weeks.
~Confusion About Capitalization~
We often get asked whether to capitalize the word following a hyphen in a title. After consulting grammar books, checking journals, and asking editors, we discovered that there is no consensus on whether one practice is more correct than another.
Therefore, both of the following examples are correct:
Predictions from Large-scale Global Climate Models
Predictions from Large-Scale Global Climate Models
We generally prefer the second option, but will post feedback from faculty on this issue.
These tips should help you to correctly use the hyphen, but when in doubt, you can always check a dictionary or a good style reference—or make an appointment at the Communications Center!
Conrey, S. M., and Stolley, K. (2010). Hyphen Use. Retrieved from the Purdue Online Writing Lab http://owl.english.purdue.edu/owl/resource/576/1/.
Hester, Z. (2010). The Hyphen. Retrieved from http://zacharyhester.com/site/articles/en_hyphen.html.
Wikipedia. (2010). Hyphen. Retrieved from http://en.wikipedia.org/wiki/Hyphen.