An apostrophe ' can be used to show possession or to denote missing letters.
Bach's Organ Works
the pupils' perceptions (the perceptions of several pupils)
the children's perceptions (the perceptions of several children)
the pupil's perception (the perception of one pupil)
the boss's authority
- For most words, add an apostrophe and the letter "s": Bach's denotes belonging to Bach; the pupil's perception denotes the perception of the pupil
- If the word is plural (ie if it belongs to more than one person/thing):
- if the plural is formed by adding "s" (ie for most plurals in English), just add the apostrophe without the final s: the pupils' perceptions denotes the perceptions of the pupils;
- if the plural does not end in "s" (eg children) add the apostrophe and the s: the children's perceptions denotes the perceptions of the children
- If a singular word ends in s (eg James, boss), it is most common to add an apostrophe and the letter "s": Ros's suggestion. However it is also acceptable to omit the final "s", particularly for longer words, or if the "s" is not sounded: Socrates' ideas; Hedges' claim.
An apostrophe can also be used in contracted forms of a word, for example:
it's for it is
don't for do not
can't for cannot
let's for let us
In formal writing (ie essays) one would not normally use these contractions.