ENGLISH LANGUAGE PUNCTUATION MARKS

Em Dash

6. English Language Punctuation - Em Dash

Like the comma, the em dash2 is used both to enclose and to separate, and like the comma, an enclosing dash needs a partner. In fact, enclosing dashes are replacements for enclosing commas in order to add emphasis. Ebbitt and Ebbitt (1982) suggest a useful philosophy toward using the dash: If used sparingly, the dash suggests a definite tone, often a note of surprise or an emphasis equivalent to a mild exclamation. If used regularly in place of commas, colons, and semicolons, it loses all its distinctiveness and becomes a sloppy substitute for conventional punctuation. At its best the dash is a lively, emphatic mark.

6. a) English Language Punctuation - Dashes That Enclose

Dashes may replace commas in enclosing interrupting elements and non-restrictive modifiers and appositives. Dashes are appropriate when a comma might be misread, for example, as a serial comma: Wrong The lasant gas, argon, and 3He were allowed to mix for 45 minutes.

In typeset material, there are two dashes: the em dash, which is the width of the letter M, and the en dash, which is half as wide. In typewritten material, the em dash is represented by two hyphens with no space around them, and an en dash is represented by a hyphen. Here the em dash will be referred to as simply "dash."


Better The lasant gas--argon--and 3He were allowed to mix for 45 minutes.

Dashes are also appropriate when the enclosed element contains internal commas: Of the lasant gases studied--argon, xenon, krypton, and neon--argon offers the most promise. The most promising lasant gas--argon, which is the lightest gas studied--produced laser output power of 4 W. Use dashes when the enclosed element needs emphasis. Enclose by dashes a complete sentence that interrupts another: Wrong Correct The one-sided spectrum, engineers call it simply "spectrum," is the output of most spectral analyzers. The one-sided spectrum--engineers call it simply "spectrum"--is the output of most spectral analyzers.

Commas are insufficient to enclose an interrupting sentence; dashes or parentheses are required. The choice of commas, dashes, or parentheses to enclose a nonrestrictive or interrupting element depends on the relation of the element to the rest of the sentence and on the emphasis it requires ( Effective Revenue Writing 1, IRS 1962): Commas (most frequently used) indicate only a slight separation in thought from the rest of the sentence. Dashes emphasize the element enclosed and clarify meaning when the element contains internal commas. Parentheses indicate that the enclosed element is only loosely connected to the rest of the sentence and therefore tend to de-emphasize it.

6. b) English Language Punctuation - Dashes That Separate

The dash is used to separate sentence elements in essentially three situations: A dash separates a group of antecedents from their pronoun that is the subject of the sentence: Argon, xenon, krypton, and neon--these are the possible choices of noble gases for use in nuclear pumped lasers. In a displayed list, a dash may separate the item from an explanatory statement: Support systems for the facility supply the following: 1. English Language Punctuation - 2. English Language Punctuation -  Air--The 600-psi system can deliver a flow rate of 300 lb/sec for 3 min. Cooling water--The closed-loop system delivers 450 gal/min at 550 psig. Gaseous propellants--Hydrogen, oxygen, and nitrogen are supplied from tanks at 2400 psia.

A dash may separate two clauses when the second amplifies or restates the first: The toughness of pseudo-maraging steel degrades at cryogenic temperatures--at -320 deg F, its Charpy impact energy is 6 ft-lb.

The colon or semicolon may also be used for this purpose. The dash is less formal than the colon and more emphatic than the semicolon. A dash may precede a phrase like that is, namely, and for example when it introduces a summarizing or explanatory phrase or clause at the end of a sentence, but a comma or semicolon may also be used (Rowland - 1962). If an explanatory clause follows the sentence, a semicolon is necessary; if an explanatory phrase follows, a comma is sufficient. If the explanatory phrase or clause receives enough emphasis by being at the end of the sentence, use a comma or semicolon, whichever is appropriate: Moderate emphasis Other random processes have average properties that vary appreciably with time, for example, the load demand on an electric power generating system. Some random processes are reasonably independent of the precise time; that is, measurements made at different times are similar in their average properties.

A dash would further emphasize the explanatory material: Emphatic Other random processes have average properties that vary appreciably with time-for example, the load demand on an electric power generating system. Some random processes are reasonably independent of the precise time-that is, measurements made at different times are similar in their average properties.

6. c) English Language Punctuation - Conventional Uses of the Dash

The dash is used by convention as follows: To separate a title and subtitle Large Space Systems Technology - 1984 Energy Efficient Transport Technology --Program Summary and Bibliography In vague or open-ended dates 1974-1980 to 19--

6. d) English Language Punctuation - Use With Other Marks

A semicolon, colon, question mark, period, or exclamation point --but not a comma-- supercede and replace a dash; that is, a semicolon, colon, or period may be the "partner" of an enclosing dash.