I have been confused about this sentence.

The first step is the phase, in which the students have to learn and write down all they know.

So comma in front of "in which" is right or wrong? Or is it optional? Doesn't matter? It's a question from an exam. I think it's wrong but the answer says it is right.

  • 2
    You can't introduce a comma after the phase, because the alerts the reader that one specific phase (out of multiple potential phases) is about to be identified by an "essential" / restrictive relative clause. You can only put a comma there if you change the reference so it already identifies the relevant phase (to be followed by a non-restrictive clause): The first step is Phase One, in which... Nov 16, 2022 at 13:03
  • This (as written, with the comma) would only be acceptable if 'phase' were being defined (perhaps a stipulative definition) here – and even then, phase should be offset (say by italicisation) as a novel usage. // 'The first stage in mitosis is prophase, in which the parent cell chromosomes condense and become many times more compact than they were during interphase.' Nov 16, 2022 at 19:27

1 Answer 1


The comma is wrong.

Commas in this context are used to introduce clauses which add information but don't change the meaning.


I called John, who is on vacation.

is OK because it tells us exactly who I called (John) and added the additional information that he is on vacation. If you omitted the clause after the comma it would not change the meaning of the first part.

In your example case if you omit the clause after the comma then you don't know which phase it is talking about: "The first step is the phase" doesn't make sense. The part after the comma is essential to the meaning and so shouldn't have a comma.

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