I'm no linguistic expert. Far from it, in fact. I do like the idea that there are rules to grammar, but I can't always remember them. My understanding of the rules is only confused by the fact that they are different in the US from this side of the Atlantic.
On Saturday, the Albany Times Union had an editorial with this for a headline: "Mr. Adams' words". I would have written "Mr. Adams's words".
The body of the Times Union's editorial has it both ways, which is clearly wrong. At least be consistent. The Times Union may not be the NY Times, but it has been around a long time and would, I'd have thought, have more pride than make such a basic error in its editorial.
That's not all that relevant to me, however. What I want to know is, which form is correct?