Possessives — Common Nouns
1. The possessive of singular and plural common nouns that do not end in an "s" or "z" sound is formed by adding -'s to the end of the word. (the child's skates).
2. The possessive of singular nouns ending in an "s" or "z" sound is usually fromed by adding -'s. A less common alternative is to add -'s only when it is easily pronounces; if it's would create a word that is too difficult to pronounce, only and apostrophe is added. (rickets's symptoms or rickets' symptoms).
2.a. A mutisyllabic sibgular noun that ens in an "s" or "z" sound drops the -'s if it is followed by a word beginning with an "s" or "z" sound. (for appearances' sake)
3. The possessive of plural nouns ending in an "s" or "z" sound is formed by adding only an apostrophe. However, the possessive of one-syllable irregular plurals is usually formed by adding -'s. (dogs' leashes, birds' migrations)
4. The possessives of proper names are generally formed in the same way as those of common nouns. The possessive of singular proper names is formed by ading -'s. (Jane's books)
4.a. The possessive of plural proper names, and of some singular proper names ending in an "s" or "z" sound, is made by adding just an apostrophe. (Massachussetts' capital, the United States' trade deficit)
5. The possessive of singular proper names ending in an "s" or "z" sound may be formed by adding either -'s or just an apostrophe. Adding -'s to all such names, without regard of the pronuinciation of the resulting word, is more common than adding just the aporstrophe. (Jones's car or Jones' car, Dickens's novels or Dickens' novels)
6. The possessive form of classical and biblical names of two or more syllables ending in -s or 'es is usually made by adding just an apostrophe. If the name has one syllable, the possissive form is made by adding -'s. (Socrates' students, Zeus's warnings)
7. The possessive of names ending in silent -s, -z, or -x are usually formed with -'s. (Delacroix's paintings)
8. The possessive of indefinite pronouns is formed by adding -'s. (anyone's rights)
8.a. Some indefinite pronouns usually require an of phrase to indicate possession. (the rights of each, the inclination of many)
9. Possessive pronouns do not include apostrophes. (mine, hers)