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Now we present the main result, that is (that is to say), the achievable region...

Could you please tell me if it's obigatory to put a comma after "that is" ( and "that is to say") or we can skip it?

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  • No, the comma is indicating something important here: If I'm not mistaken, an appositive. Just like you can't remove the comma after 'result', you can't remove the comma after id est.
    – M.A.R.
    Dec 6, 2015 at 19:04

1 Answer 1

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The comma is used for setting off nonessential explanations. If an explanation or definition occurs as an appositive it should be set off with commas:

When the nonessential explanation is not at the end of the sentence, like in your example, it should be set off with a pair of commas.

If the nonessential explanation is placed at the end of the sentence then only one comma is needed.

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    "Now we present the main result, that is the achievable region AR." "Now we present the main result, that is, the achievable region AR, where we suppose..." Is this what you mean ?
    – din
    Dec 7, 2015 at 17:07
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    Yes,that would be correct. A comma can change the sense of a sentence, @din.
    – Lucian Sava
    Dec 7, 2015 at 17:47
  • I don't really see why this answer applies to the question. Even with only one comma, it seems clear that the definition is an appositive?
    – Rastapopoulos
    Mar 27, 2019 at 17:08

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