A Guide to Hyphens and Dashes

By Mark Nichol

This post details the purposes of various horizontally aligned typographical symbols.

Hyphens perform various functions, including the following:

  • They link standing compound words (mind-set, self-respect).
  • They are used with some prefixes (anti-inflammatory).
  • They represent expression in isolation of a prefix or a word element (pre-, -er).
  • They link spelled out numerical terms representing different place values (twenty-four).
  • They link words in phrasal adjectives preceding but not following a noun (“short-term investment,” “off-the-cuff remark”) and when combining similar-looking constructions that begin with comparative adverbs such as better, much, and well (“best-kept secret”)

Some style guides (but not this site) recommend that phrasal adjectives be hyphenated regardless of their position, and a few such expressions (such as far-reaching) are always hyphenated regardless of position or style authority. Also, a letter space should never intervene when a hyphen connects two words or numbers, except when suspending the first use of a word common to two or more phrasal adjectives (“fifteen- and thirty-day increments”).

Hyphens are often introduced when new compounds are created, including in technological vocabulary, but such terms usually become closed compounds (though there are exceptions, such as mind-set, mentioned above, and light-year). Some terms that include letters linked to nouns retain hyphenation (A-list, T-bone, X-axis). Omission of a hyphen in email is trending, but similar terms such as e-commerce resist this evolution.

Em Dash
The dash, technically known as an em dash (to distinguish it from the en dash, described below), is used to indicate parenthesis when more emphasis is intended than indicated by a comma or a pair of parentheses. One dash is employed to when the wording expresses an attempt to get attention (“Look—a squirrel!”) or to indicate a sudden break in syntax and the parenthesis ends a sentence (“What I meant to say is—hey, are you paying attention?”) Similarly, it can replace a colon (“You have three options—fight, flight, or surrender”). Two dashes are employed when the parenthesis occurs mid-sentence (“The original version of the document—the one I hold here—is worded differently”).

The dash is also employed to set off the identification of the source of an epigraph (“‘The only thing we have to fear is fear itself.’ —Franklin D. Roosevelt”). Also, one or more dashes may indicate redaction of all or part of a word or name in order to avoid identification or euphemize profanity (“The target was identified as ———”; “Ms. A—— is not unacquainted with scandal”; “Well, I’ll be d——ed!”).

Dashes are usually closed—that is, they are set with no preceding or following letter spaces—but some publishers prefer to format them open. Some, too, out of ignorance or apathy or for the sake of simplicity (as in the case of some newspapers), use a single or double hyphen in place of an em dash—or, because they prefer its size, employ an en dash. (This is a valid design decision, but use of a single or double hyphen appears amateurish and should be avoided.)

En Dash
The en dash, always so called to distinguish it from the default em dash, which is often referred to simply as a dash, has two functions:

  • representing a range of numbers or a time span (“Read pages 15–37”; “John Smith [1936–2012] is not listed”; “These figures represent revenues during the first quarter [January–March]”) as a substitute for through
  • serving as a substitute for a hyphen in a compound term (“Pre–Civil War conditions sometimes prevailed”; “The United States–Mexico border is nearly two thousand miles long.”

(These distinctions are, again, sometimes ignored.) The en dash is employed for the latter use because “pre-Civil War conditions” implies “before the Civil” rather than “before the Civil War” and “the United States-Mexico border” appears to refer to a united border between States and Mexico rather than one between the United States and Mexico.

Plus Sign
A plus sign (+) is employed in mathematics and other disciplines to indicate addition or positive numbers, and in lay usage it may modify a letter grade or qualify a blood type. It is sometime used informally to indicate a value greater than the stated one, as in “I would say 50+ people attended.” (Formally, “I would say more than fifty people attended” is better, and a direct quote would be better represented as “I would say fifty-plus people attended.”)

Minus Sign
A minus sign (–) is a distinct symbol used in digital displays of mathematics and other disciplines to signal subtraction or negative numbers; like the plus sign, it may be used in designations of letter grades and blood types. However, a minus sign is often represented by a hyphen or an en dash in print or online.

Multiplication Sign
A multiplication sign (×) is used almost exclusively in mathematics and in isolated functions in notations in biology and history. In lay usage, the letter x generally takes its place.

Division Sign
The division sign, officially called an obelus, was replaced by the dagger mark (†) as a reference sign and now pertains exclusively to division in mathematics.

Equal Sign
An equal sign (=) represents equivalence and is occasionally used in informal writing in place of equals.

A tilde (~) usually functions to denote a variation in pronunciation of certain letters in various languages, but it also serves in informal writing to signal approximation, as in “We continued along for ~20 miles.”

The underscore (_), employed on typewriters to create underlines, survives now mainly as a symbol in email addresses, URLs, and computer code.

11 Responses to “A Guide to Hyphens and Dashes”

  • D.A.W.

    Then there is the confusing name of the programming language C++. In the different versions of “C”, the double plus sign means to add one to a variable. For example, the expression “N++” means to take the value of N, add one to it, and then store that in the old place for N. If N is 16, then N++ means to change the value of N to 17.
    Much more sensible is the way that things are done in the BASIC language: Let N = N + 1.
    This tells the computer to add one to N, and then store that in the old location for N.
    The name “C++” means to improve C to the next higher level. There never was a language named “C+” – because of all this silliness.

  • D.A.W.

    Yes, there are several different symbols for “approximately equal to”, including the two stacked tildes that venqax mentioned, and the equal sign with the tilde that I mentioned, and more.
    In textbooks, it mostly depends on what kind of type-setting stuff that the printer/typesetter has available.
    For a lecturer in the classroom, it depends on the personal preference of the instructor.
    I have seen another symbol printed for this meaning, and it is an equal sign with a dot above its middle. I do think that this one fell out of favor some decades ago. Still, there are old textbooks that are still around.

  • venqax

    I thought that 2 tildes together, kind of a squiggly equal sign, also meant “approximately equal to”. Like this sign without the bottom straight bar: . I can’t find any reference for that anywhere, however. That symbol, , with the bar underneath does also mean “approximately equal to”. Maybe I am thinking of that, just recalling the 2 tildes (or swung dashes, actually, I think.)

  • D.A.W.

    All of these hyphens in the terminology indicate multiplication:
    One newton-meter = one joule of energy.
    One dyne-centimeter = one erg of energy.
    One watt-second = one joule.
    One light-year = about 10 trillion meters.
    One volt-ampere = one watt of power.
    One ampere-ohm = one volt.
    One ampere-second = one coulomb of electric charge.

  • D.A.W.

    An equal sign with a tilde above it means “approximately equal to”.

  • D.A.W.

    Notice these hyphenated items:
    A-shirt, B-grade (not the best), C-clamp, D-ring, E-ring (in the Pentagon), F-15 Eagle, G-2 (intelligence), HH-60 Jayhawk, I-beam, I-95, K-meson, KC-135, L-bar, M-4 (a British motorway), N-ray (thought of in France, but these do not exist), O-ring (notorious from the space shuttle “Challenger”), P-3C Orion, RF-4 Phantom, S-IC, S-IVB, T-shirt, T-bar, U-2, V-22 Osprey, W-particle, X-2, X-15, Y-bar, YC-14, Z-particle.

  • D.A.W.

    Note: “Omission of a hyphen in email is trending.”
    Any quantity can be trending up, trending down, or trending about the same (or constant).
    Hence, the catch phrase of “X is trending” is meaningless.
    What we have to blame for this are the poor quality of education, for the general population, in mathematics, science, and technology; and the lack of “critical thinking” therein.

  • Dale A. Wood

    In the MKS system, some of the “derived units” are the watt, joule, newton, liter, farad, henry, ohm, pascal, and volt.
    In the cgs system, some of the “derived units” are the
    dyne, erg, gauss, and oerstead. The cgs system is not used too much anymore.
    In both the MKS system and the cgs system, there are more units for radioactivity, such as the curie and the roentgen, and more units for electricity and magnetism, such as the ampere, coulomb, tesla, and weber.

  • Dale A. Wood

    In the realm of measurement and units, the hyphen usually indicates multiplication, as in light-year, newton-meter, foot-pound (energy), pound-foot (torque), dyne-centimeter.
    The exceptions are in two subsets of the metric system: the meter-kilogram-second (MKS) system and the centimeter-gram-second (cgs) system.

  • Dale A. Wood

    I agree with Venqax on this completely. Those “differences” are merely unnecessary complications.

  • venqax

    I have to confess that I don’t see the real need for the distinction between hyphens, em dashes, and en dashes. They seem to be a concern for printing, perhaps, but not actually for writing. Am I missing something?

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