Question

I want to write about this person whose last name is "Williams"

if I want to talk about a book he wrote do I write "Williams's" or "Williams" or "Williams'" book

Thanks

Answer 1

You can either use
Williams's
or
Williams'

I prefer the first -- but as this website explains, consistency in this case is more important than which form you choose.

http://grammar.ccc.commnet.edu/grammar/possessives.htm