Apostrophes have two main purposes, to form possessives and to mark contractions. Correct usage of apostrophes is an easy way to prevent a loss of points on your papers. Unless you are showing possession or a contraction an apostrophe should not be used.
Possessives mark ownership or possession of an object or trait.
For a singular possessive the writer need only add ’s to the end of the word (even if it ends in an “s”).
For plural possessives make the word plural and add ’s. If the word ends in and “s” just add an apostrophe.
Using apostrophes with dates:
1950 references the year directly. 1950s refers to the entire decade.
1950’s is a reference to some fact or occurrence that belongs to the decade (e.g. The Twist was a 1950’s dance).
Though it may seem odd to have a number and letter next to each other without punctuation, the plural has no apostrophe.
Contractions are a way of marking omitted letters in informal writing.
|do not/don't||I am/I'm||am not/ain't|
|is not/isn't||should have/should've||never/ne're|
|come on/c'mon||you have/you've||of the clock/o'clock|
Contractions should generally be avoided in academic writing. The main exception is creative writing, where presenting a dialect or writing in an informal tone contributes to the story, but don’t overuse them. There are contractions that have fallen out of use and into misuse, such as “ain’t.” But that doesn’t mean they can’t still be used.