In general, we use apostrophes to indicate possession or contracted forms.
- Apostrophes for possessive forms of nouns
The possessive form of a singular noun is marked by an apostrophe followed by s.
the manager’s report the lecturer’s hypothesis This rule applies in most cases even with a name ending in –s.
the PAS’s response Erasmus’s success If a plural noun already ends in –s, the apostrophe is used alone.
the students’ work (several students) the teachers’ room (all the teachers) Note that the apostrophe is also used in expressions of time periods.
eight weeks’ time two weeks’ leave Degree titles should be written with an apostrophe followed by s.
bachelor’s degree master’s degree But note the exception: doctoral degree, not doctor’s degree.
Do not use apostrophes to indicate a decade, a plural acronym or the plurals of figures.
the 1990’s the 1990s URL’s URLs 747’s 747s - Apostrophes for contractions
Use apostrophes for contractions (you’re for you are, don’t for do not, it’s for it is or it has) but note that contractions are far less common in formal texts than they are in informal writing.