I'd like to know how to explain the rules for use of possessive "s" to describe the quantity of something, as in, "two hours' work" to an English learner.

This answer at english.stackexchange.com, suggests the phrase "...worth of..." is omitted. I don't think anything's necessarily omitted, so it's more precise to say that "worth of" can be added between the "'s" and the noun without changing the meaning.

This sentence is grammatical and idiomatic:

People need between seven and nine hours’ sleep every day.

But these feel somewhere between unnatural and nonsense even though they work fine with "worth of" inserted:

There's 5 million dollars' jewellery behind that glass.

I drove through three thousand kilometres' desert in the last couple days.

I bought a salary's farmland to retire on.

From these, I'm guessing that this possessive "s" structure can only be used naturally with units of time.

My questions:
Can the possessive "s" with this function reliably be replaced with "worth of"?
Does this structure work only with units of time?
Does this structure work reliably with any noun measured by units of time?
What's the name of this structure's function for easier Googling?

  • I have 8 hours’ sleep every night = I have 8 hours of sleep every night = I have a sleep of 8 hours every night. The sleep doesn't "possess" the timespan, any more than the timespan possesses the sleep. Also note that there are quite a few separate written instances of between seven and nine hours sleep in Google Books, but I don't see any with an apostrophe (as opposed to, say, a full day's work). Sep 11, 2021 at 11:52
  • @FumbleFingers Ngrams currently puts the apostrophe ahead of no apostrophe, but the issue is certainly not settled.
    – gotube
    Sep 11, 2021 at 23:18
  • You can't search NGrams for a sequence of more than 5 words, and in any case there wouldn't be enough instances of "between [number] and [number] hours sleep" to work with. Having said that, I've just compared the 4-word sequence need eight hours' sleep with and without apostrophe, and you're right that the apostrophe seems to be more common. I think that's some kind of artefact - I can't find any actual examples when I drill down. Sep 12, 2021 at 11:50
  • 1
    I'm particularly taken by the first result returned by this Google Books search: I secured two amendments to the House bill city of Washington to do eight hours work for eight hours' pay, which changed this system of taxation. Sep 12, 2021 at 11:58
  • ...note that there are two other results for the above search that show the full text, and neither of them have any apostrophes. Lord knows what the US politician (or his stenographer) thought they were doing only putting an apostrophe before pay, but not work. Whatever - so far as I'm concerned, that's the only relevant apostrophe I've found so far, and it was clearly written by someone who hasn't got a clue how to write properly! Sep 12, 2021 at 12:02

1 Answer 1


Your intuitions are correct that only the temporal measures can be possessive without "worth". CGEL p. 470 calls these measure genitives:

[46] [an hour's delay], [one week's holiday], this [hour's delay], a second [one hour's delay], the [one dollar's worth of chocolates] he bought

Genitives of this kind measure just temporal length or value: we do not have, for example, *They had [a mile's walk] (spatial distance) or *We bought [a pound's carrots] (weight). Value measures take the noun worth as head, while the temporal ones allow any semantically appropriate noun as head. An alternative means of expressing measure is to use a compound adjective, as in a [two-hour delay], a [five-mile walk], an [eight-pound baby], etc.; this is less restricted than the genitive, though it is not admissible with worth.

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