Possession for Common nouns

There are a few rules that state how to use apostrophes when showing possession:

1. If a singular noun doesn’t end in –s, we add -‘s to show possession. (The girl’s hat is on the table.)

2. If a singular noun ends in –s, we add -‘s to show possession. (The hostess’s cake was delicious.)

3. If a plural noun doesn’t end in –s, we add -‘s. (The women’s phones were turned off.)

4. If a plural noun ends in –s, we only add the apostrophe (‘). (The girls’ dresses were too long.)

5. If multiple nouns possess another noun, we add –‘s at the end of the final noun. (The boy and girl’s toy was found in the garden.)

 

Possession for Proper nouns 

As in the case of common nouns, the possessive of singular proper nouns is formed by adding –‘s while the possessive of plural nouns ending in -s is formed by adding an apostrophe only.

Example:
Maria’s shoes are on the shelf.
Ross’s hobby is paleontology. (Ross – singular proper noun)

The Joneses’ garden is great. (Joneses – plural proper noun as in members of a family called “Jones”. If someone’s name ends in “s” we must add “-es” to form the plural.)

Some writers will say that apostrophe -s after singular proper nouns that end in –s (such as Charles) or common nouns that end in double “s” (such as witness) is no longer necessary and that we should only add the apostrophe to show possession while other writers insist that we actually hear an “-es” sound when dealing with possessive forms, so an apostrophe –s is needed (witness’s point of view).
Both approaches are accepted; just make sure you are consistent with the one you’ll choose.