Apostrophes

Using apostrophes to show possession

You use an apostrophe to show that a thing or person belongs or relates to someone or something: instead of saying 'the party of Ben' or 'the weather of yesterday', you can write 'Ben’s party' and 'yesterday’s weather'.

master’s degree, bachelor's degree   

Use an apostrophe to spell ‘master’s degree’.  The ‘s’ in ‘master’s’ indicates both a possessive (the degree of a master) and a collective singular, not a plural.

If you are writing of a specific degree, you should capitalise 'master' and avoid creating a possessive:

The same rules apply to a ‘bachelor’s degree’:

The title of these degree qualifications is 'Master of Science' and the general title is 'master’s degrees', so a student of a master’s degree is a master’s student.

The plural of 'bachelor's degree' or 'master's programme' does not affect the placing of the apostrophe, because the plural only concerns the second part of the term ('programmes', 'degrees').

NOTE: on UT websites, try to avoid using the word "programme" or "degree" after "bachelor's" and "master’s":

Personal names that end in –s

With personal names that end in -s: add an apostrophe plus s when you would naturally pronounce an extra 's' if you said the word out loud:

Note that there are some exceptions to this rule, especially in names of places or organisations, and it is sometimes a question of personal choice and judgement:

Plural nouns that end in –s

With a plural noun that already ends in -s: add an apostrophe after the s to mark a possessive:

Plural nouns that do not end in -s

With a plural noun that doesn’t end in –s: add an apostrophe plus s to mark a possessive.

Possessive pronouns do not need apostrophes

The only cases in which you do not need an apostrophe to show belonging is in the group of words called possessive pronouns and with the possessive determiner his. These are the words: his, hers, ours, yours, theirs (meaning ‘belonging to him, her, us, you, or them’). 

Possessive use of ‘it’:  It’s or its?

These two words can cause a lot of confusion: many people are uncertain about whether or not to use an apostrophe.

Rule: ‘its’ (without an apostrophe) means ‘belonging to it’:

Rule: 'it’s' (with an apostrophe) is a contraction of two words, meaning ‘it is’ or ‘it has’:

Apostrophes showing omission (contractions)

An apostrophe can be used to show that letters or numbers have been omitted.

It also shows that numbers have been omitted, especially in dates.

EXAMPLE: The Berlin Wall came down in the autumn of ’89 (short for 1989).

Common mistakes and some exceptions

The general rule is that you should not use an apostrophe to form the plurals of nouns, abbreviations, or dates made up of numbers: just add -s (or -es, if the noun in question forms its plural with -es).

two exceptions

There are one or two cases in which it is acceptable to use an apostrophe to form a plural, purely for the sake of clarity. 

1. You can use an apostrophe to show the plurals of single letters

2. You can use an apostrophe to show the plurals of single numbers

Reference

Oxford Living Dictionaries. 'punctuation/apostrophe'. Retrieved from https://en.oxforddictionaries.com/punctuation/apostrophe.