Correct use of hyphen, en dash, or em dash in compound words [duplicate]

Question

Possible Duplicate:
Dashes: - vs. – vs. —

I know that there are many sources on the use of dashes both on tex.sx ( Dashes: - vs. – vs. — ) and in the real world (Wikipedia: Dash). But there are still cases where I do not know the correct dash to use.

Compound words
many-body nature
electron-electron interaction
ion-atom collision
higher-order terms
non-negligible amount
short-lasting event
quasi-adiabatic reaction

Names
Slevin-type source
Maxwell-Boltzmann distribution

Elements
carbon-14

Answer 1

Here is Bringhurst's take.

Almost all of your examples should be hyphens. Most interword dashes should be hyphens. The exception, as Joseph pointed out in the comments is cases like Maxwell–Boltzmann. This is a case of two different people's names joined up, and perhaps needs distinguishing from Maxwell-Boltzman as a double-barrelled name. Although only the keenest, typographically attuned eye will spot the difference…

En dashes should be used for number ranges 34–42 without space. As a "phrase marker" – a kind of alternative to the parentheses – the en dash should have space either side.

The em dash can be used to introduce dialogue

— Like this?
— Yes, like this.

And as an indicator of interruption, like thi—

Longer dashes can be used for repeated names in bibliographies.

Answer 2

Some typographers suggest (i.e. they consider it a possible way to do things, not a compulsory one) that you can use en-dashes (--) when you are not using a compound word or expression, but two different words that are in some sort of logical relationship (opposition, link). So for instance: "ion--atom collision", "London--Washington relationship", but "non-negligible".

Also, you can use an en-dash if one the words is already a compound word: "Pulitzer prize--winning", but "Selvyn-type source" or "short-lasting event" (they are expressions, not words of their own). It may not apply when the "compound" word only has a prefix in it: "non-English-speaking".

The logic behind it is that you should use a longer sign when the link between the two elements of the phrase is weaker, and a shorter one when they are very much related. For the same reason, many (more) typographers recommend using an en-dash between digits that indicate a range (see Bringhurst p. 80--81, with a dash).

Note: Few typographers openly endorse this practice, and few talk about it at all – but it does not mean it should not be used. Matthew Butterick is one that does recommend it (Typography for Lawyers, p. 49).

Some people recommend it only insofar as you do not use em-dashes (---) in your document, e.g. for dialogues and asides.