Uses Of Apostrophes

We use apostrophes (’) for three main reasons.

Missing letters

It is used in writing a contraction to show the place of the omitted letters.

can’t (= cannot)
it’s (= it is)
I’d (= I would/had)
who’s (= who is/has)

Possessives

We use apostrophes in writing most possessives.

the girl’s father
three miles’ walk
two weeks’ work
my parents’ wedding

Possessive determiners and pronouns do not have apostrophes.

This is yours. (NOT …your’s.)
Whose is that coat? (NOT Who’s …)

Special plurals

Apostrophes are used in the plurals of letters, and often of numbers and abbreviations.

Mind your p’s and q’s.
It was in the early 1960’s.