I recently had to explain the correct use of the apostrophe to some people, and thought it might be of interest to others.
Herewith my interpretation of when to use, and when not to use, an apostrophe. Hope it is of help.
The baker went to town. (This is a simple statement about a person who is a baker by trade going to town.)
The baker’s dog went to town. (This is telling us that a dog, belonging to the baker, went to town. i.e. the apostrophe describes ‘possession’. The dog is owned by the baker.)
The Bakers went to town. (This is another simple statement about a family called Baker who went to town. The ’s’ indicastes it is plural, no possession, therefore, no apostrophe.)
The Bakers’ dog went to down. (This is telling us that a dog, which belonged to a group of people of the Baker family (plural, hence the ’s’), went to town. again, apostrophe describes possession.)
The Bakers and their dog went to town. (Another simple statement. The family called Baker went to town with their dog. No possession, just two separate things going to town.)
The baker’s gone to town. (This is telling us that a bloke who is a baker has gone to town. It is a contraction of ‘baker has’, so needs an apostrophe to indicate a missing vowel.)
Golden rule is that an apostrophe is used:
when referring to something owned by someone.
If it is singular, the apostrophe comes before the ’s’ (baker’s); if it is plural, the apostrophe comes after the ’s’ (Bakers’).
exception is if the singular (say John Jones) ends in an ’s’, in which case it comes after the ’s’; e.g. John Jones’ dog
When two words are joined together, and some letters (usually vowels) are missing; eg it’s for it has.