This is a common question/problem for my students. Even published authors bicker about the rules for apostrophes in forming possessive nouns. While the rules may vary from publisher to publisher, the classroom grammar books (assuming they are actually used–but don’t get me started on that!) agree on three basic rules for making possessive nouns.
Rule #1–If the noun is singular, add ‘s. (Examples: the child’s toy, Chris’s journal, the bus’s wheels)
Rule #2–If the noun is plural and ends with an -s, add an apostrophe after the s. (Examples: the four buses’ wheels, the cats’ toys, the trees’ leaves)
Rule #3–If the noun is plural and does not end with an -s, add ‘s. (Examples: the children’s toys, the men’s ties, the women’s shoes)
The sticky point comes with Rule #1. Some people don’t like the way singular nouns ending in -s look when ‘s has been added. For example, Jesus’s teachings. They want to write it as Jesus‘ teaching.
I’ve seen this in print numerous times, and I think the problem stems from the fact that Jesus’s requires a repetition of the s sound three times in a row. However, the grammar books I’ve used have all said to simply add ‘s to all singular nouns. One grammar book even noted that you didn’t need to pronounce the extra s if it became too cumbersome.
Either way, I’m sure I’ll be correcting apostrophe usage for as long as I teach English. 🙂
At least my students don’t use apostrophes to make plurals like the poor writer who made the sign in the photo to the right.
Every time I see major punctuation abuse like this, a teeny part of my soul dies.