Dashes are much more than just lines. They have very specific grammatical jobs. There are actually three types of dashes (excluding track and field events). The typographical dashes are the hyphen [ - ], the en-dash [ – ] and the em-dash [ ].
Hyphen is used to created compound words like mother-in-law and full-time job. They're also used to connect words that are broken in print by line breaks. When using hyphens in this manner, break words only at their appropriate syllables. If in doubt where to do this, consult a dictionary.
Note there are certain words such as online/on-line and byproduct/by-product that can be written with or without hyphens. This depends which style guide you're using as a reference. Whichever style you choose, consistency is paramount.
Hyphens have also traditionally been used in the United States and Canada to separate the sections of telephone numbers, but with the proliferation of new media, hyphens are frequently replaced with dots or spaces, giving us three choices:
For the time being, take your pickhyphens, dots or spacesbut whatever is chosen, be consistent throughout the document. Putting parentheses or round brackets around area codes seems atavistic nowadays, when required dialing of area codes is so commonplace.
555 555 1234
The en-dash [ – ] is longer than the hyphen. In Microsoft Word, you can create an en-dash by pressing CTRL + the minus key on the number pad on a PC or by pressing Option + the dash key on a Mac. The en-dash is used to separate number sequences, such as 7 – 9 p.m. or pages 167–182. In fact, the AutoCorrect feature in Microsoft Word automatically changes hyphens to en-dashes when they appear between numbers.
Finally, em-dash [ ] is the longest dash. It's used to expand or separate thoughts, to indicate a verbal pause or to designate a series within a phrase. Here are examples:
In August 2007, Osmo Vänskä will return to the BBC Promsthe world's largest classical music festival.
To create an em-dash in Microsoft Word, press CTRL + ALT + the minus key on the number pad (PC) or press Shift + Option + dash key (Mac).
Martin Scorsesedirector of "The Departed," "Goodfellas" and "Raging Bull"was nominated six times before winning his first Oscar.
Sources: Gregg Reference Manual, Bloomsbury Grammar Guide and the UPI Stylebook and Guide to Newswriting.