I wrote the following sentence:
"Tell me when when you know." (Note the double "when".)
The intended meaning was that of: "tell me when you want me to be there, when you know when you want me to be there". I was then thinking: I feel like it would read a lot nicer if instead, I wrote "tell me when, when you know"; but my question is, is the comma there optional or necessary? In other words: is "tell me when when you know" grammatically correct without the comma?

As alternative examples where this is less bold (but which I think are the same in principle): Let's say someone asks me to, say, run some software on their computer, and I want to ask them for instructions when they have a moment; so I say: "tell me how when you have a moment". As in, "tell me how to do it when you have a moment". Is a comma necessary here? ("Tell me how, when you have a moment.") Or is it just a matter of styling at this point?
And if so, then is that the same as the previous case, or is it different for some reason? (It seems to me to be the same case: if instead of asking for "how" I asked for "when", i.e: when I should run the software, then the question would be "tell me when when you have a moment," which brings us to a similar when-squared predicament.)

2 Answers 2


Comma is not strictly needed.

But: clause and phrase boundaries in spoken speech are rendered with changes in pitch and short pauses.

Tell me when when you have a moment

Speaking this sentence, the two when's would be pitched/accented differently signaling a break.

In written text, you don't have the benefit of that additional channel of information. Commas come to the rescue.

Just looking at this without any additional context makes me think the double-when might be an error, and I would then gloss over it and assume the single when is intended.

So technically it's a style issue but it's something you'll always want to do.

  • Thank you very much :) Could you please give me some keywords that I can use when discussing/Googling about this? For instance, how I could call the relationship between "tell me when" and "when you have a moment"? So I could say something like "a comma between an X and a Y is optional". I assume it has to do with the clause and phrase that you've mentioned but I want to make sure.
    – Shay
    Commented Feb 3, 2022 at 14:55

When spoken there is a slight pause between the 2 when's, do the comma is correct. If you don't pause the sentence is much harder to understand.

  • Hi :) I know the sentence is easier to read with the comma, and that the sentence with the comma is fine; what I'm asking is whether the sentence without the comma is also grammatically correct (despite being hard to understand). Thanks for the answer!
    – Shay
    Commented Feb 3, 2022 at 16:37

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