A hyphen is a short line used in compound words and double-barrelled names. There’s one there in “double-barrelled”, which is a compound word. Hyphens don’t usually have spaces before or after them.

A dash is a long line used as a punctuation symbol. It acts in a similar way to commas or brackets to separate a piece of text — like this. Dashes do usually have spaces before and after them.

Hyphens in compound words

WRONG
The court requested BIG Polska S.A. to deliver the files of the claims — handling proceedings.

RIGHT
The court requested BIG Polska S.A. to deliver the files of the claims-handling proceedings.

WRONG
Her name is Anna Ponsonby — Smythe

RIGHT
Her name is Anna Ponsonby-Smythe

In recent decades the hyphen has been going out of fashion. Compound words like “land-owner” or “co-operation”, which always used to require a hyphen, are now commonly written “landowner” and “cooperation”. The idea that “lifesciences”, “knowhow” or “healthcare” are routinely written as one word might still have the power to shock members of the older generation.

However, some compound words will always need hyphens. The example I use above is “claims-handling”. The alternative — “claimshandling” — is unreadable because of how we normally read “sh”. The rule here is that you should use a hyphen when you link two or more words to make a compound modifier. A modifier adds information to another word like an adjective. In the above example the word “proceedings” is modified by “claims-handling”. Here are some other examples:

a business-class ticket
a two-week notice of termination
third-party insurance
a steel-producing plant
a five-year-old boy
a free-of-charge service
a personal-data processor
a light-grey car

Obviously none of these compound modifiers could be written as one word.

The importance of the hyphen is illustrated by the last two examples. While “a light-grey car” only describes the car’s colour, “a light grey car” is a light car (i.e. a small road car as opposed to a larger vehicle), which is grey in colour. Similarly “a personal-data processor” is someone who processes personal data, while “a personal data processor” is a data processor who works only for one particular person.

Hyphens in numbers

When writing numbers like 42, 67 or 99 in words, always use a hyphen:

forty-two
sixty-seven
ninety-nine

Numbers such as 2,456,887 should therefore be written in words as follows:

Two million, four hundred and fifty-six thousand, eight hundred and eighty-seven.

Hyphens and prefixes

Use of hyphens with prefixes is a difficult area. Words like “pre-war”, “re-live”, “non-compete” and “anti-abortion” need them, but words like “prejudge”, “reinsure”, “nonviolent” and “antisocial” do not.

The rule is rather a vague one: if the word looks OK and reads OK without a hyphen, don’t use one. Otherwise put one in.

A good example of where one is necessary is “re-send”. The past tense is “re-sent”. “Resent” means something entirely different. E.g. “I resent your attitude”, i.e. I don’t like/do not accept your attitude.

Dashes

Dashes are mainly used to separate pieces of text called strong interruptions. (Commas are used in the same way to separate weak interruptions.) Here are some examples:

The company has fulfilled all its tax obligations — at least that’s what the CEO says.

We finally completed the transaction yesterday — after six long months of negotiations.

If the strong interruption comes in the middle of the sentence you need a pair of dashes:

The documents — enclosed for your convenience — show that the evidence so far presented is not complete.

Remember to include a space before and after the dash.

How to type them

In Microsoft Word, the hyphen/underscore key (between “0” and “=” on the keyboard) produces a hyphen.

However, it will automatically turn into a dash when you press the space bar after the word that follows it, provided that there is also a space before and after the hyphen. But you have to write something after the hyphen.

You can also make a dash by using Ctrl “-” (on the number keypad) or Alt 0150 (also using the number keypad).

PowerPoint or Outlook may behave like Word — depending on the version you’re using. Alternatively you may wish to adopt the American convention of typing two hyphens to denote a dash.