The English language, like all other languages, is constantly changing and evolving. Archaic terms are discarded and new words are created all the time. The same can be said about grammar, sentence structure, and word choice.
For example, purist may tell you that split infinitives are always wrong, but they’re becoming increasingly accepted and even preferred under some circumstances. There’s just something to be said about choosing the right words for the right effect. Similarly, there’s something to be said about choosing words for simplicity’s sake.
Growing up, I was always taught that “they” referred to a plural. When I say that “they” went to the store, the understanding is that more than one person went to the store. If just one person went to the store and I was unsure of the gender, I was taught that I should say “he or she” went to the store or “he/she” went to the store. As you imagine, this can get quite messy very quickly.
More and more, the “singular” they is becoming an accepted alternative to the he/she construction. In fact, there’s an entire Wikipedia entry on the matter and the discussion is quite extensive. The two main uses for the singular they are when there is an indeterminate gender (most common) and when there is an indeterminate number.
The victim said they were attacked in the alley.
Anyone still in the store at midnight will be told they have to leave.
If we adhered to the old rules and listened to the purists, the first sentence would read: “The victim said he/she was attacked in the alley.” Some traditionalists may use a “generic he” in place of “he/she,” but that raises issues of gender inequality. That’s how we came to “he/she” in the first place.
So, moving forward, can “they” be used as a singular? The short answer is yes, but depending on the context, it may or may not be appropriate. Just as there are all sorts of conflicting rules about the Oxford comma, the same can be said about the singular they. For anyone who wants to use the singular they, they’ll just have to make a judgement call on their own.
I have no problem using they in the singular. In fact I have always considered it “cross gendered.”