Learn English – Comma after introductory words, phrases, clauses: unacceptable, obligatory or optional

commasprepositional-phrases

I am no native speaker and always confused about the comma in introductory phrases, in particular in prepositional phrases. Is there any hard rule when a comma must be set? If I make a google search for certain phrases, I often find both variants. Typical examples where I am not sure whether a comma must be set are:

  • First[ly][,] I must phone mother

  • In this case[,] we must…

  • For simple problems[,] the algorithm…
  • From Lemma 1.2[,] we obtain…
  • For a typical user[,] the algorithm…
  • In our theory[,] we…
  • A dark line on the horizon[,] the mountain range we were headed for seemed somehow not as threatening as when we had started out on the trip.
  • Avidly reading her novel[,] Jane did not notice that her stop was approaching.
  • To be sure[,] it is not easy to see a solution.
  • When you get to Rome[,] give me a ring.

Best Answer

Larry Trask’s advice in cases like this is to see what happens if you remove from the sentence the words marked off by the comma. If you are left with a meaningful sentence, then the comma is appropriate. If no meaningful sentence remains, you don’t need the comma.

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