1. Use 's to show that a singular noun is possessive. Although usage is changing (some writers add only the apostrophe), you should apply this rule even when the singular noun already ends in "s." Exceptions are historical figures whose names end in es.	the defendant's motion Charles's costume Dr. Jones's prescription Moses' ten commandments Ulysses' men
2. Use 's to show that a plural noun not ending in "s" is possessive.	the women's movement alumni's contributions people's votes
3. Add only an apostrophe to make plural nouns possessive.	students' questions parents' concerns companies' profits the Oswalds' family vacation
4. Do not add an apostrophe to a noun that is not possessive.	Singular: The scientist’s research was controversial. Plural: Scientists have claimed that global warming is an imminent threat. Plural possessive: Scientists’ previous theories have been disproved. Singular: Mr. Jones was not home last night. Singular possessive: Mr. Jones’s car was vandalized. Plural: The Joneses were not home last night. Plural possessive: The Joneses' car was vandalized
5. Do not add an apostrophe to a possessive pronoun.	The problem is yours, not hers [not her's]. The firm failed to disclose its [not it's] assets.