Last week, we gave you some general rules on possessives. This week, let's focus on possessives of proper nouns.
General Rule: The possessive of singular nouns is formed by the addition of an apostrophe and an s, and the possessive of plural nouns (except for a few irregular plurals) by the addition of an apostrophe only. The general rule for the possessive of nouns covers most proper nouns, including most names ending in sibilants (a definite "es" or "ez" sound):
- Dickens's novels
- Ross's land
- Descartes's works
- Vaucouleurs's theorems
- In Jesus' name
- Moses' leadership
- Ramses' tomb
- Xerxes' army
- Euripides' plays
- Minneapolis and Saint Paul's transportation system
- but Chicago's and New York's transportation systems
- The National Review's fortieth year of publication
You will find that some proper nouns, especially when there are other s and z sounds involved, turn into clumsy beasts when you add another s: "That's old Mrs. Chambers's estate." In that case, you're better off with "Mrs. Chambers' estate."
There is another way around this problem of clunky possessives: recast the sentence using the of phrase to show possession. For instance, we would probably say the "constitution of Illinois" as opposed to "Illinois' (or Illinois's) constitution."
Source: The Chicago Manual of Style, 14th edition