Pronouns are on the front burner of language change at the moment. As such, we get a lot of questions about them.
For example, a listener recently asked if you should say, "They are going to the store," or "They is going to the store," when referring to one person.
Since it's perfectly fine to use "they" in this manner, we need to address the question of whether the verb should be singular.
It’s helpful to remember that there are two different constructions for singular "they."
In one construction, gender is irrelevant or unknown. This singular "they" goes back hundreds of years and has consistently used plural agreement with the verb. You might say, "You should ask someone who knows where they are going." In this example, "someone" refers to one person, but we still use the plural "they are."
This construction makes more sense when you think about the pronoun "you." This is another pronoun that, in most varieties of English, kept the same verb agreement when it took over the singular function in addition to the plural. You can use "you are" to refer to one person, or you can use it to refer to lots of people.
The other singular "they" construction is the non-binary "they." This is the pronoun we use when there's a specified person who does not identify as "he" or "she" and prefers "they/them" pronouns. With this construction, we tend to see the same plural agreement as the other construction: "They went to the store on their own."
This construction is pretty new and some people may still be getting used to using it. However, as Professor Anne Curzan says, it's important to use the pronouns that people prefer.
"Using people's pronouns is about respect, in the same way that using people's names is about respect," Curzan says. "If someone says their pronoun is 'they,' then that's their pronoun."
The question remains, will we ever start to see "they is" for the non-binary singular "they"? Maybe. It could become a way to distinguish this particular "they" from other uses. Right now though, we tend to see "they are."
However, as Curzan likes to remind us, language changes.