Apostrophes should not be used with possessive pronouns because possessive pronouns already show possession—they don't need an apostrophe. His, her, its, my, yours, ours are all possessive pronouns. However, indefinite pronouns, such as one, anyone, other, no one, and anybody, can be made possessive.

Showing possession When any noun, whether it’s a person, place, or thing, possesses something, you always add an apostrophe plus "s." If, however, the noun is already plural with an "s" on the end, simply add an apostrophe. Otherwise, if the noun is plural but doesn’t end with an "s," add an apostrophe plus "s."

Tip #1: If two nouns are equally showing possession, only use an apostrophe on the second noun. Tip #2: If two nouns are showing separate ownership, use an apostrophe on both nouns. Tip #3: When using a hyphenated noun, only make the final word of the hyphenated noun possessive.