At least I haven't yet been able to imagine a context in which there is a clear semantic difference between "that that" and "which that". No hardware warnings, either. I've always been a bit troubled by the double-that, and I know that some spelling checkers object, but as far as I can recall none of them has ever recommended "which that" as a replacement.

  • 1
    There is no actual construction “that that” any more than there is a construction “hardware warnings” they are simply two words that are placed next to each other in order to achieve the intent of the speaker. That that is not clear to everyone is somewhat concerning.
    – Jim
    Commented Mar 19, 2019 at 21:45
  • Well, I want to add a general broad comment thanking people for their prompt and accurate responses. In particular, I agree that the cited examples are correct, though the recent ones I had encountered "in the wild" were different. Mostly I feel distrust of my own language hardware now...
    – shanen
    Commented Mar 20, 2019 at 10:23

3 Answers 3


The first valid hit I found on Ngram:

I only know that that slice of attention caused me to actually shape a personality around the tale.

And right below it:

He assured me that that was his destination, so I hopped in.


And as I grow up I would know that that is the person I am suppose to be with for the rest of my life!

In none of those cases is replacing with "which that" valid.

  • @Tuffy - Your point being?
    – Hot Licks
    Commented Mar 20, 2019 at 0:42
  • My comment was merely to see if four 'that's are possible. I have deleted it as off topic.
    – Tuffy
    Commented Mar 20, 2019 at 12:08
  • @Tuffy Buffalo ** 8!
    – Hot Licks
    Commented Mar 20, 2019 at 12:10

which that may occur as a accidental collocation ("the toy which that child holds is made of wood"), but for what you probably mean you want it the other way 'round: that which.

Your first that is a demonstrative pronoun and remains the same. Only the second is a relative pronoun which can be replaced (and in my opinion should be replaced) with which.

That which does not kill us makes us stronger.

  • I don’t think that’s what Shanen is asking about – since your case doesn’t work with that that at all, it’s not a case of that that having been replaced with which that. (Though if I’m reading you correctly, you’re implying that that that doesn’t kill us… would be grammatical to you? To me, it’s not just a matter of style: it is completely ungrammatical in my head.) Commented Mar 19, 2019 at 21:47
  • @JanusBahsJacquet I would never use that (dem) that (rel); but my dislike for it is not universal. I think it is by descriptive canons grammatical. Commented Mar 19, 2019 at 22:05


"I know that that isn't the answer" wouldn't work with "which that": "I know which that isn't the answer".

From the answer to this question: How do you handle "that that"? The double "that" problem

We have the subordinating that (“I know that this is the answer.”) is doubled up with a demonstrative pronoun that (“That is not the answer.”) or an adjectival that (“That answer is not it.”).

Depending on the exact sentence you can often replace the subordinating that but not always with "which".

Not the answer you're looking for? Browse other questions tagged or ask your own question.