2015 was a big year for the little pronoun they and its slide into use as a singular pronoun.
First, in December, the Washington Post admitted the singular they into its style guide, saying it is fine for Post writers to use they as a singular pronoun for transgender people and to avoid awkward sentences. Then last week, hundreds of linguists at the American Dialect Society annual meeting voted for the singular they as the 2015 word of the year.
To be clear, what we’re talking about is how to complete a sentence such as
If a resident wins the lottery …
At this point, writers struggle because English has a big, gaping pronoun hole—we have no universally accepted word to describe a person if we don’t know whether that person is male or female. We could write If a resident wins the lottery, he should at least buy everyone ice cream, she should at least buy everyone ice cream, he or she should at least buy everyone ice cream, or something else.
Add in transgender people and people who don't identify with either traditional gender, and the gaping pronoun hole becomes an even bigger problem.
Alternating Between the Pronouns 'He' and 'She'
A listener named Betty summed it up best by saying that he or she seems too awkward and he alone seems sexist. I’ll add that exclusively using she also seems sexist, the hybrid s/he seems silly and awkward, and switching between he and she can be downright confusing to readers. A listener named Bryan called switching between he and she “whiplash grammar,” which I loved.