Sorry, I don't think I can use all the grammatical terms right, so I'll illustrate:

Peptide adsorption curves may cross [...] results in the inversion of peptide elution order.

I've found a lot about "which" and "that" in this question, and it says that generally those are interchangeable, but I haven't seen this particular use case mentioned there. (After writing this it occurred to me that the linked question discusses "which" and "that" as conjunctions, whereas this question is about them as relative pronouns. I got this from this answer. Correct me if I'm wrong) The only thing that might be applicable is the "rule of thumb" that

"Commas, which cut out the fat, go with which, never with that."

On this basis, "which" should be the only correct option, because that gap needs a comma. Is that so?

  • 2
    Whoever downvoted, could you please comment on what is bad in this question? I'm not an experienced EL&U user, so I could use some advice about improving the question. Aug 26, 2012 at 21:22
  • possible duplicate of When is it appropriate to use 'that' as opposed to 'which'?
    – Robusto
    Aug 26, 2012 at 22:12
  • 1
    @Robusto I have linked to that question, cited an answer to it, and made a comment about my question being different from it. I also asked to correct me if I was mistaken about that. Could you please provide some clarification or do you find a close vote good enough? Aug 26, 2012 at 22:27
  • Lev, I didn't down-vote you. We have had so many questions regarding which vs. that that I voted to close this question as a duplicate, but that isn't the same as a down vote. Obviously my due diligence was lacking, but this site's search makes it very hard to find questions at all, much less ones in which your search terms are very common words like which and that. Mine is the only close vote so far, so your question appears to be in no danger.
    – Robusto
    Aug 27, 2012 at 0:28

1 Answer 1


Which is the correct relative pronoun you should use in your sentence, because you have a main clause ("Peptide adsorption curves may cross"), followed by a non defining, or non restrictive, relative clause that gives additional information or, as per your example, the consequence of what has been mentioned before.

I had never heard of the so called "rule of thumb", but I like it and I'll try to pass it on to others in order to try and sort out this kind of difficulty.

  • 1
    Perhaps the OP has in mind the convention that non-defining relative clauses are set off by commas. Aug 26, 2012 at 21:31

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