Why do we need "an" in these sentences below?

  • I run an additional three-tenths of a kilometer.

  • I write an additional 5 words.

As an English learner, I would omit "an," because it's illogical for me. I see plural forms, so my first reaction is to omit the articles. I would say:

  • I run additional three-tenths of a kilometer.

  • I write additional 5 words.

Please explain me the differences between these sentences, because my all grammar knowledge has just fallen.

I found a semi-explanation here, does it make any sense?

  • 1
    I think "an additional five words" treats those "five words" as a whole.
    – Cardinal
    Jun 26, 2017 at 12:21
  • @Cardinal might be right. I guess you could then say "I ran two additional 5 kilometres". You definitely need the article in your examples, but if you were to swap the number and the word "additional", or remove the number entirely (but keep a plural noun/unit) you would definitely remove the article.
    – SteveES
    Jun 26, 2017 at 13:02
  • 2
    Think of it as I run an additional (distance of) three-tenths of a kilometer and I write an additional (amount of) five words.
    – Davo
    Jun 26, 2017 at 13:52
  • @Cardinal Does it change the meaning of the sentence? Or maybe it doesn't play a role, and I'm good with all these options? Jun 26, 2017 at 19:34
  • 1
    I think using singular form, when referring to the amount of something, is more common. However, I think there wouldn't be any significant difference if you use the plural form.
    – Cardinal
    Jun 26, 2017 at 19:48

1 Answer 1


"an (additional)" treats whatever follows as a whole.


  • I run an additional three-tenths of a kilometer.
  • I run an additional distance.


  • I write an additional 5 words.
  • I write an additional paragraph.

If you want to remove "an", you can use:

  • I run additionally three-tenths of a kilometer.
  • I run three-tenths of a kilometer more.


  • I write additionally 5 words.
  • I write 5 words more.
  • I write 5 more words. (which is actually much better than previous)

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