Is the following sentence correct?

We refine it when we can revisit a vertex.

The "it" refers to nothing (it seems to be the dummy pronoun), but the sentence seems correct to me. I think "it" is needed, because "refine" is a transitive verb. What I want to say in this sentence is that we refine the circumstances when we can revisit a vertex.

Is there some grammar rule that would back my claim that the sentence is correct?


  • If you're sure it doesn't refer to anything (i.e. - something which you refine in the specified circumstances), just don't include it. The text is at the very least "unusual" (I have absolutely no idea what it might mean, in any real-world context), but syntactically it's perfectly valid with it (something gets refined in that situation), or without it (we refine / specify more precisely the time at which we can or will be able to revisit a vertex). Commented Sep 4, 2018 at 12:36
  • Thanks, FumbleFingers, for your comment. The Oxford dictionary says that that "refine" is only transitive, so I thought that "it" is required, even though it is kind of dummy. But then I checked the Merriam-Webster dictionary, and indeed "refine" can be intransitive too, and has the meaning you described and that I need. That solves my problem. Thank you! Commented Sep 4, 2018 at 14:45
  • Much depends on your exact definition of a "transitive verb". Q. What does an oil refinery do? A. It refines! Strictly speaking we should say that's an intransitive usage, but in practice A's response would be nonsense if it weren't for the contextually implied direct object (It refines oil). And consider the full OED's most recent citation for the "intransitive" form: As their taste refines, jewellery buyers usually turn their attention towards small, delicate things. Same thing there - contextually implied the jewellery buyers refined their tastes. Commented Sep 4, 2018 at 15:36
  • Thank you, FumbleFingers, again for your insight! I wish I could mark your comments as the answer to my question. Commented Sep 5, 2018 at 6:48
  • I didn't post an "Answer" because I had already voted to close the question as "Unclear" (precisely because you haven't edited the question to clarify exactly what meaning you intend the example sentence to convey). Note that if I cast a closevote like that, I hope (but don't necessarily expect) that the question will be amended to give more details - in which case I will happily reconsider my vote, and cancel it if appropriate. Commented Sep 5, 2018 at 13:25

2 Answers 2


"it" refers to nothing

No! This is not true. The "it" probably refers to a term mentioned in the previous sentence. If this was indeed a standalone sentence, then "it" shouldn't be used.

  • Thank you, QuIcKmAtHs, for your answer. After your answer, and FumbleFingers comments, I decided just to remove "it" from the sentence. Initially I thought that "it" served as a dummy pronoun, but it's better just to remove it. Commented Sep 5, 2018 at 9:02

The verb refine is "awkward" here. It could mean 1) purify, distil, make more concentrated (referring to something mentioned earlier) or 2) fine-tune, revise, make more precise (referring to the timing of the visits).

There's also ambiguity as to whether we're talking about times when it would be possible to visit (regardless of whether we do or not) or times when we actually manage to visit (by implication, with some difficulty). But I'll ignore that aspect.

The short answer to OP's question is that if there is a "something mentioned earlier" (sense #1 above), the word it is required, to refer back to whatever that "something" is. If not (sense #2), it should not be present.

But I think perhaps what's really confusing OP is better illustrated by looking at a similar construction involving when and an ambiguous / dummy it...

I like [it] when you (infinitive verb phrase)
I like it when you smile (10 hits in Google Books)
I like when you smile (5 hits)

...where both forms do occur, but they mean exactly the same thing. As the figures suggest, we usually do include that "dummy pronoun", but I think it would be pointlessly pedantic to argue that either version is more "correct". Consider this more "generic" example...

I fall asleep as soon as I go to bed at 11 o'clock every night, but I always know [it] when you come home after midnight

...where know could be replaced by various alternatives (hear, resent, hate, like, record1,...). And in all cases, the word it is optional - if present, it can be thought of as a "forward reference" to the activity specified later (your smiling, your coming home late), or simply a "dummy".

My feeling is this kind of optional "dummy it" can only occur with verbs of perception / reaction. It certainly can't apply with OP's verb refine, or with any "synonyms" for either of the two senses I defined in the first sentence of my answer.

1 I thought it was worth including something like record here even though it requires a bit of "creative context" to make sense (perhaps an unhappy wife recording her drunken husband's behaviour, to support her pending divorce application). The point being that recording the time of coming home is effectively a "reaction" to that event.

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