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Hyphens, En Dashes, Em Dashes
Q. I know an em dash marks an interruption in dialogue:
“I thought I might—”
“Might what?” she demanded.
But what happens if the same person speaks after the interruption? For example, “Can you bring me a— socket wrench, is that what you call it?” Is that space after the em dash correct?
A. Your space after the dash does makes a little bit of sense—but it doesn’t quite work. Because even if there is some logic to it, will people read that space as you intended it? Very possibly not, and definitely not if the dash happens to fall at the end of a line—as dashes are prone to do. Any editorial decision that is likely to be missed by readers or obscured by context—or that could be lost if quoted (for example, by someone following a style that puts a space before and after a dash, which would render your example meaningless)—is one that should be reconsidered.
So, either delete the space:
“Can you bring me a—socket wrench, is that what you call it?”
Or, if you want to somehow convey the extra pause or break that the space is trying to communicate, mark the interruption in some other way:
“Can you bring me a . . . socket wrench—is that what you call it?”
“Can you bring me a—what do you call it?—a socket wrench?”
“Can you bring me a”—he hesitated—“a socket wrench? Is that what you call it?”
In sum, be wary of any editorial innovation that relies on a mere space to get across the intended meaning. It has a good chance of being lost in translation.