One of my students wants to know...why do we say "a fortnight's holiday" or "a fortnight's time"...he insists that the fortnight does not belong to the holiday in the first instance and that it does not belong to "time" in the second instance. He thinks we should say " a fortnight holiday/time. Now I know that I would choose the former as being correct but how do I explain it to him?
I know the answer. It is an easy to understand explanaton that I am looking for!
Thanks in advance,
I would call this the "temporal genitive", with a sense "of the duration of" ("a holiday of the duration of a fortnight").
Rather than "belonging to", which is only one sense of the genitive, I would think of it as "relating to". Thus:
1. The boy's book = the book relating to the boy.
2. Today's news = the news relating to today.
3. Goat's milk = milk relating to goats.
4. A day's pay = pay relating to a day.
5. An hour's wait = a wait relating to an hour.
Does that help?