I have seen many questions on this, but all the answers seem to address the example—how the use of em-dash may be avoided using some other forms of punctuation in that particular example—and not the concept in general. And it feels like I have a very particular example at hand that seems like it would really be better with a pair of em-dash, and the latter seemingly must be followed by a comma.

If P₃ has to lie—and it has to lie to improve its chances beyond 𝜀₁—, using one of its given superpowers will be its best strategy, given that they are ultimately potent and incur the lowest risk possible of getting caught.

Options considered:

  1. Dropping the comma after the em-dash: This is no good. The sentence without the em-dashes and the supplementary expression within must make sense, and it doesn't without that comma.
  2. Replacing em-dashes with parentheses: Works, but given how exclamatory the supplementary expression is, parentheses around it doesn't suit as well.
  3. Replacing the first em-dash with comma and leaving out the second: Makes it hard to connect the if-clause to its then-clause.
  • #1 is the classic use of paired em-dashes. You may have misunderstood, but this is good to use. Commented Feb 4 at 23:46
  • @YosefBaskin How so? "If P₃ has to lie using one of its given superpowers will be its best strategy, [...]" sounds totally off to me, which is what you get when you take out the em-dashed expression. Commented Feb 4 at 23:49
  • No, native speakers don't see it that way. The feeling of a big break remains: "If P₃ has to lie [MAJOR PAUSE BIGGER THAN A COMMA] using one of its given superpowers will be..." If you don't buy that, don't use the pair, and don't use the dash & comma together. Commented Feb 4 at 23:53
  • 1
    #2 is equally good, with a comma: "If P₃ has to lie (and it must, to improve its chances beyond 𝜀₁), using one of its given superpowers will be..." Commented Feb 5 at 0:05
  • No, there should not be a comma after the em dash. You can use a pair of commas instead, or the pair of em dashes alone. Commented Feb 5 at 3:16


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