The corner of Twitter that’s interested in English usage has recently been all aflutter over that popular topic, they used as a singular pronoun, as in “If a patron doesn’t like the opera, they are free to leave.” It seems to have been sparked by this Wall Street Journal article by @bgzimmer. The article suggests that copy editors are increasingly willing to accept this usage.
I suspected that this issue would soon come knocking on my door. Sure enough, I then saw the following tweets by @NealGoldfarb:
E.g., in a contract between a human and a corporation: "Each party shall pay their own expenses…"
— Neal Goldfarb (@NealGoldfarb) April 8, 2015
In my general writing I’ve long used they as a personal pronoun. Would I use it in contracts? Not at the moment, and for the same reason that I don’t use contractions in contracts. (On that subject, see this 2008 post.) It’s not a matter of right or wrong, more a matter of tone: contract language is limited and stylized, so I find it a bit dissonant to introduce in contracts the most informal usages of general writing.
In this context, I would use his/her/its. Joking! My default is actually to use that party’s.