A hyphen (-) may sometimes be called an "en dash" or "figure dash"; a dash (-- or —) may sometimes be called an "em dash" or "horizontal bar." (The "en" & "en" names derive from typesetting: a hyphen is the same length as "n"; a dash is the same length as "m.")
Hyphens and dashes are frequently confused with each other because in handwriting they may look much the same, and a typewriter or keyboard uses the same key to make either—once to make a hyphen, twice to make a dash.
A recent confusion of hyphens and dashes: when a media announcer (or anyone) reads aloud a web or email address containing a hyphen, they usually say "dash" instead of "hyphen." For instance, an email or web address written "small-fry.com" would be spelled out vocally as "s-m-a-l-l-dash-f-r-y-dot-com." Being a snoot, I spell out such an address as "s-m-a-l-l-hyphen-f-r-y-dot-com," but doing so only confuses my listeners. Not the first time hyphens or dashes annoyed a teacher, who then annoy everyone else!
Differences in visual appearance:
+ differences in function:
More on appearances of hyphen and dash: You'll see variations in style or appearance for several reasons:
To make a hyphen on a typewriter or keyboard, hit the hyphen key once with no spacing before or after. Examples: mid-September; all-inclusive.
To make a dash on a typewriter or keyboard, hit the hyphen key twice with no spacing before or after. Word Processors normally convert the two hyphens into a single long dash as long as you don’t add any space before, after, or between.
(either typography is acceptable by MLA standards)
Functions of hyphen and dash—when to use a hyphen, when a dash.
“If you take hyphens seriously, you will surely go mad” (Oxford University Press style manual). Why?
Hyphens often develop "compound words," which are a standard feature of English and other Germanic languages. Examples: red-haired, nitty-gritty, soft-spoken, close-up, U-turn.
But when or whether to hyphenate words is complicated by the evolution of "compound words,"
Two words brought together as a compound may be written separately, written as one word, or connected by hyphens. For example, three modern dictionaries all have the same listings for the following compounds:
Another modern dictionary, however, lists hairstylist, not hair stylist. Compounding is obviously in a state of flux, and authorities do not always agree in all cases.
Evolution of compound words—first with a hyphen, then without.
Touchtone or touch-tone phones: early in this compound's career in the 1970s and 80s, "touch-tone" was hyphenated. Now that the compound is familiar, the hyphen has disappeared: "touchtone." Until recently, many people still wrote "email" as "e-mail." "Key-pad" was hyphenated for a while but now is not: "keypad."
Daydream, gravestone, stepfather, highway, and washcloth are all compound words that have lost their hyphens, but when these terms were first coined, they were probably written as day-dream, step-father, etc., and we can still imagine writing them thus. Saucepan might be spelled sauce pan or sauce-pan. Even most English teachers won't be especially anxious about such variations.
To check whether a compound noun is two words, one word, or hyphenated, you may need to look it up in the dictionary. If you can't find the word in the dictionary, treat the noun as separate words. Otherwise, as long as the words are the right words, hyphenation errors aren't usually a big deal and can be easily edited.
When to hyphenate
Generally, hyphenate between two or more adjectives when they come before a noun and act as a single idea.
(compound adjective in front of a noun; hyphenated because
normally you wouldn't use the word "making" without "decision"; if the two
words need each other to function sensibly, they're hyphenated.)
friendly little girl
brightly lit room
HYPHENATE ADJECTIVES FORMED FROM TWO OR MORE WORDS
"in-depth analysis," but "Let's discuss this in depth." (both correct)
"The corporation was having balance-of-payments difficulties," but "The corporation was experiencing difficulties with balance of payments." (both correct)
"Private-sector wages have risen slowly," but "Wages for the private sector have risen slowly." (both correct)
HYPHENATE ALL COMPOUND NUMBERS FROM TWENTY-ONE TO NINETY-NINE.
HYPHENATE ALL SPELLED-OUT FRACTIONS.
Use a hyphen to avoid confusion or an awkward combination of letters:
re-sign a petition (vs. resign from a job)
semi-independent (but semiconscious)
shell-like (but childlike)
Use a hyphen with the prefixes ex- (meaning former), self-, all-; with the suffix -elect; between a prefix and a capitalized word; and with figures or letters:
also use a hyphen with MOST WORDS THAT BEGIN with anti, non and neo. Thus anti-aircraft, anti-fascist, anti-submarine (but antibiotic, anticlimax, antidote, antiseptic, antitrust); non-combatant, non-existent, non-payment, non-violent (but nonaligned, nonconformist, nonplussed, nonstop); neo-conservative, neo-liberal (but neoclassicism, neolithic, neologism). (Again you are likely to see any of these words either with or without a hyphen.)
Hyphenate some words that become unmanageably long with the addition of a prefix. Thus under-secretary, inter-governmental, director-general, under-secretary, secretary-general.
Use a hyphen to divide words at the end of a line if necessary, and make the break only between syllables:
HYPHENATE TO AVOID AMBIGUITIES
fine-tooth comb (most people do not comb their teeth)
third-world war (a war between third-world nations)
SEPARATING IDENTICAL LETTERS:
Ranges of Values
The hyphen or en dash is commonly used to indicate a closed range of values, meaning a range with clearly defined and non-infinite upper and lower boundaries. This may include ranges such as those between dates, times, or numbers. Examples of this usage may include:
Relationships and connections
The hyphen or en dash can also be used to contrast values, or illustrate a relationship between two things. Examples of this usage may include:
Sometimes a pair of words that are hyphenated in one place won't be hyphenated in another.
Phrases that have verb, noun, and adjective forms usually appear as separate words when used as verbs and as one word when used as nouns or adjectives.
Let's break down
the numbers. (verb)
When adverbs not ending in -ly are used as compound words in front of a noun, hyphenate. When the combination of words is used after the noun, do not hyphenate.
The actress who accepted her award
was well known.
decision was finally made.
a one-way street > Just walk one way and
don't turn. (both correct)
simple constructions do not use hyphens to link adverbs to participles or adjectives:
But if the adverb is one of two words together being used adjectivally, a hyphen may be needed:
The ill-equipped regiment was soon repulsed. All well-established principles should be periodically challenged.
The hyphen is especially likely to be needed if the adverb is short and common, such as ill, little, much and well.
Less-common adverbs, including all those that end with -ly, are less likely to need hyphens: "Never buy a richly decorated sofa." (No hyphen is correct.)
dash (-- / —) (sometimes called "em dash" or "horizontal bar")
dash is a mark of
separation stronger than a comma, less formal than a
colon, and more relaxed than parentheses."
(Wm Strunk, Jr, and E.B. White,
Elements of Style)
Dashes are usually regarded as an "informal" type of punctuation. Thus dashes often represent informal, conversational, or dramatic speech:
"I can't believe what you're telling me—that's ridiculous!"
"Books, paper, pencils—many students in nineteenth-century America lacked even the simplest tools for learning."
In such uses, the dash marks a break of thought or some similar interpolation stronger than the interpolation marked by parentheses or commas. (interpolation = something introduced or inserted)
Dashes can take the place of other punctuation marks, especially
When dashes replace commas, semicolons, colons, and parentheses, they usually indicate added emphasis, an interruption, or an abrupt change of thought.
Danger: When writers first learn to use dashes, they often misuse or overuse them. If you like the effect of a dash, save it for when you really want it. The more you use it, the less power it will have.
Dash instead of ellipses ( . . . ) for dramatic pause or shift, plus or minus follow-up:
The Dash is used to indicate a conclusion without expressing it: "He is an excellent man but—"
It is used to indicate what is not expected or what is not the natural outcome of what has gone before: "He delved deep into the bowels of the earth and found instead of the hidden treasure—a button."
"By trying we can easily learn to endure adversity—another man's, I mean." (Mark Twain)
Use the terminal dash to suggest that a statement suddenly breaks off; use the terminal ellipsis to suggest that it trails away.
"As your Commanding Officer, I'll have to say no, but as your friend, well—."
(adapted from Winston Weathers and Otis Winchester,
The New Strategy of Style.
"But I—But you said— . . . wait, what?" stammered Edna.
"What he said was true—or so I thought."
"Of course, I'll sign a prenuptial agreement—as long as it's in my favor." (In this case, the dash replaces a comma, making a more emphatic pause or shift.)
"Shirley gave me a terrible haircut—and she still expected a tip!" (In this case, the dash replaces a comma, making a more emphatic pause or shift.)
Dash instead of a colon (:)
"London looked like the moon's capital—shallow, cratered, extinct." (Elizabeth Bowen, "Mysterious Kor." The Demon Lover and Other Stories, 1945)
"Those privileged to be present at a
family festival of the Forsytes have seen that charming and instructive sight—an
upper middle-class family in full plumage."
The Man of Property, 1906)
Dash in place of a semicolon (;)
"I pay the bills—she has all the fun."
Dash instead of parentheses (( )) or commas (,) when setting off interpolative clauses or phrases--the dash-use sometimes called "double dash."
"Oscar came home from work—he
was a construction worker—and turned
on the air conditioner."
"You are the friend—the only friend—who offered to help me."
"I'd better pass my test—it's ninety percent of my class grade—or I'll have to go to summer school."
"The moral flabbiness born of the
exclusive worship of the bitch-goddess success. That—with the squalid cash
interpretation put on the word success—is
our national disease."
Between a citation and the authority for it there is generally a dash: "All the world's a stage."—Shakespeare.
Use of Dashes with Other Punctuation
generally don't mingle with other punctuation marks, with the exception of
quotation marks, exclamation points, and question marks. If the material set
off by dashes is an exclamation or question, those marks are included before
the second of the pair of dashes:
"His job—we all know that he likes to keep busy!—was to tend the children while their parents attended church."
Various materials on this page adapted from http://www.grammarbook.com/punctuation/hyphens.asp, http://owl.english.purdue.edu/owl/resource/576/01/, http://www.englishforums.com/English/RulesForUsingHyphens/gqxx/post.htm, http://en.wikipedia.org/wiki/Dash, http://grammar.about.com/od/d/g/dashterm.htm, http://www.grammarbook.com/punctuation/dashes.asp, http://www.wikihow.com/Use-a-Dash-in-an-English-Sentence, & http://www.examples-help.org.uk/punctuation/the-dash.htm.