Sorry, Zeality, but I heartily disagree on the double s possessive bit. I also disagree on the use of the singular they...it's the only gender neutral pronoun we have, and while it is typical plural, we might as well use it in the singular as well since one doesn't exist and it's helpful for various writings, like when you want to do your best to hide the gender of a person. (That comes in handy in a lot of stuff, like online Mafia games.)
I envy you and your language sometimes, being able to hide the gender of a person without sounding rather strange would be perfect for so many things. Just imagine you being male, telling your parents you found a partner, yet don't tell them it's a "he"(using this "neutral gender"). Man, the look on their face would be priceless
Not that I ever made this experience; I wouldn't even dare to think about it, who knows if the parents turn out to be homophobic? Well, But I think that face would be worth the damnation.
