If I'm not sure about the gender of Brown may I write "Brown was merry and their cat was sad"? [duplicate]
Solution 1:
Definitely not, at least according the rules for singular they that I absorbed when I was growing up. The relevant rule is that you cannot use singular they for somebody you refer to by name. So you can say:
Somebody named Leslie called, and they want you to call them back. (The referent is someone.)
But not
Leslie called, and they want you to call them back. (The referent is Leslie.)
This grammatical rule seems to be changing, in that more people are finding these constructions acceptable nowadays, especially since some alternatively gendered people want to be referred to as "them" (something I would have a hard time doing). However, I would still recommend rewriting the sentence to avoid breaking this rule.
And one last comment: if you don't know Brown's sex, how do you know that he or she was merry (unless it's hard to tell Brown's gender by looking at him or her)?