"we will provide you with three weeks severance"
or is it
"we will provide you with three weeks' severance"
Here is what I found:
plurals – Be attentive to subject-verb
agreement problems that can arise when
plurals are used as subjects. To form the
possessive case of plural nouns ending in –s or
–es, add only an apostrophe.
• Two weeks’ severance pay was
available to some workers.
There are three uses of apostrophes:
1. Forming the possessive case
2. Indicating omissions in contractions
3. Forming certain plurals
Forming Possessive Case:
One way to tell if you need to make a possessive is to turn the phrase around and make it an “of the” phrase. For example:
the boy’s hat = the hat of the boy
the clock’s hands = the hands of the clock
(1) Singular Nouns and Indefinite Pronouns: add ‘s.
This land is considered everyone’s property.
“The Monk’s Tale” is one of Chaucer’s Canterbury Tales.
(2) Singular Nouns Ending in –s: add ‘ or ‘s.
In this case, it is also acceptable to add only an apostrophe to the end. The decision should be made on the pronunciation.
James’ idea of fun is a day spent outdoors.
Maris’s mother has a birthday coming up.
(3) Plural Nouns Ending in –s: add ‘.
Laid-off employees received two weeks’ severance pay.
The three girls’ father bought them a puppy.