Hyphens, Dashes, and Colons

If you were writing instructional material, which of these four examples would be correct?

A  Medication dosage -3 ML
B  Medication dosage — 3 mill
C  Medication dosage-3 Ml
D  Medication dosage – 3 ml

Yes, this is a kind of “trick question,” because the answer depends on the meaning. In this example, the variations are with the dashes and abbreviation for milliliter. Conventions and formatting matter when it comes to defining meaning! Does example A mean you reduce the dosage by 3 milliliters? Does example B mean the dosage is 3 million?

There are three main kinds of dashes, or more accurately, two common kinds of dashes and a hyphen. They are defined by different lengths, and look like this:
Em dash —
En dash –
Hyphen ‐
To this list we should also add the colon (:).

The rules for each of these four characters can get very detailed (and overwhelming,) and I refer you to the Chicago Manual of Style for a detailed discussion of each use case. However, when it comes to defining meaning and proper use of conventions, the following guidelines will give you the information you need most of the time.

Em Dashes

An em dash should be used to set off text, often in the same way you would use commas, but with a stronger emphasis. If it were music, I would compare it to a longer pause to set off the musical phrase a bit more. I prefer the formatting used in Robert Bringhurst’s The Elements of Typographical Style — by including a space between the dashes — which I find more attractive. The Chicago Manual of Style—with formatting I find cramped—does not. Either spacing can be considered correct and will not change the intended meaning. You can also use an em dash instead of a colon, as long as the dash is preceded by a complete phrase. Again, the difference is a matter of emphasis — the em dash just stands out more. You can contrast that with the more low-key colon: a quieter choice.

En Dashes

Next in line is the shorter en dash. An easy way to remember the difference between an em and en dash is that the letter n (en) is not as wide as the letter m (em). The en dash is primarily used to separate continuous numbers, or to otherwise signify an inclusive range; you can think of it as a substitute for “from” or “to.” You would use it to alert employees that they must choose their benefits between December 01–24, and they have to choose between Plans A–D.
It has become common to use a dash in a definition list in lieu of a colon. In that case, I use an en dash, as the usual em dash substitute for a colon just seems too long.
Em dash — This is an em dash, but it seems too long in this list.
En dash – This seems just right.
Hyphen ‐ This seems too short.
Colon: This is a safe choice, but becoming less popular.

Hyphens

A hyphen is used primarily to either hyphen-
ate words, or connect non-continuous numbers, for example, a social security, phone, or serial number: 1534-6345-7345. The hyphen is commonly used as a minus (-) sign, although some character sets provide a separate character for this. As seen in the confusion of the A–D example that started this section, it is important not to use a hyphen unless you are hyphenating, or signifying either subtraction or a negative number.

Use the Pause as the Guideline

Without grabbing The Chicago Manual of Style, or some other reference, how can you remember when to utilize each symbol? It often comes down to how much of a pause you want between letters or numbers. A hyphen essentially says this is one unit, and there is very little to no pause. Electronic mail became E-mail, which in turn became email. The hyphen was a transition to one word, but when said out loud, there is no pause in either E-mail or email. By the same token, when hyphenating a word at the end of a column, there is no signifi-cant pause. If you live at 113-B Maple Street, the same consideration applies; it is symbolically and literally describing a “unit.” It is the place for a hyphen.

Phone numbers, like (415) 555-8426, were based on an area code (415) for a region, a physical exchange location (555) within that region, and an individual phone line (8426) within that exchange. To signify that farther-to-closer relationship, the formatting turned into (415) 555-8426. The use of parenthesis emphasized that if you called outside your area code, you would get charged extra. Since out of area code calls are not the big deal they used to be, and switches are now digital, notice how phone numbers have often morphed to 415-555-8426? The main purpose now is giving you a place to briefly pause so you do not have to read, remember and say ten numbers in-a-row. Since the numbers are non-continuous, it is again the place for a hyphen.

If the relationship is not so snug, then the next step up from a hyphen is an en dash. You would not say the package is arriving between “December FirstSixth” (December 01–06.) You would insert a pause: “First to the sixth.” In this case, the en dash is a substitute for “to.” The numbers are a range, so it is the place for an en dash.

When the relationship calls for an explicit pause, like a comma, it is time for the long em dash. Longer pauses are a matter of emphasis, the longer the pause — the greater the emphasis. Colons can sometimes be substituted for em dashes, but they are not used in pairs as em dashes sometimes are, the text after the colon must end the sentence or phrase.

Conclusion

When trying to sort out the appropriate type of dash, remember the length of the pause is best clue to its appropriate use. When you are dealing with no pause, as in hyphenation, or non-continuous numbers that are part of a unit, use a hyphen. For a short pause, as in a range, or continuous numbers, use an en dash. Finally, for a longer pause, similar to a comma, use an em dash. If you want something a little less strong, or more economical in space, consider a colon. If you are still not sure, look at the Chicago Manual of Style, or a similarly authoritative source.

This article is an excerpt from my work-in-progress book “More than Pretty — Designing Effective Training and Help Documents.”