Dashes are excellent devices for emphasizing key material and for setting off explanatory information in a sentence. They can also be used to indicate where each item in a list begins and to separate paragraph headings from succeeding text. See HEADINGS, LISTS, and PUNCTUATION.
Dashes primarily appear as an em dash—meaning that the dash is about as wide as the letter “m.” Dashes also appear as an en dash, which is as wide as a letter “n.” The en dash has only a few uses:
- Appendix D–2
- pages 120–122
Most word-processing software programs have a special code for dashes so that dashes appear as a solid line, not two separate hyphens. Using this code makes your text appear to be typeset, not typed on an old-fashioned typewriter. When you use a dash between two words, leave no space on either side of the dash. See SPACING.
NOTE: Traditionally, hyphens are even shorter than en dashes, but many software programs have the same code for hyphens and en dashes. See HYPHENS.
Dashes link introductory or concluding thoughts to the rest of the sentence.
Dashes linking thoughts emphasize the break in the sentence. Dashes often make the first thought the most important part of the sentence:
- Winning the Navy’s supercarrier contract—that’s what the Franklin Shipyard needed to remain solvent.
Dashes can act like colons, however, and throw emphasis to the last part of the sentence:
- We subjected the design to rigorous testing—but to no avail because stress, we discovered, was not the problem.
Often, the information following the dash clarifies, explains, or reinforces what came before the dash:
- We consider our plan bold and unusual—bold because no one has tried to approach the problem from this angle, unusual because it’s not how one might expect to use laser technology.
Dashes can also link otherwise complete sentences:
- The technical problem was not the design of the filter—the problem was poor quality assurance.
Dashes interrupt a sentence for insertion of thoughts related to, but not part of, the main idea of the sentence:
- Octoronase had been undergoing clinical tests—all these were done abroad—for 3 years before the patients were withdrawn from the trial.
In this example, parentheses could replace the dashes; with parentheses, the sentence becomes slightly less emphatic. See PARENTHESES.
Dashes emphasize explanatory information enclosed in a sentence:
- Two of Barnett’s primary field divisions—Industrial Manufacturing and Product Field Testing—will supervise the construction and implementation of the prototype.
In this example, commas or parentheses could replace the dashes. The commas would not be as emphatic as dashes; the parentheses would be more emphatic than commas, but less emphatic than dashes. See PARENTHESES and COMMAS.
Dashes link particulars to a following summary statement:
- Reliability and trust—this is what Bendix has to offer.
- Developing products that become the industry standard, minimizing the risk of failure, and controlling costs through aggressive management—these have become the hallmarks of our reputation.