Singular they is the use in English of the pronoun they or its inflected or derivative forms, them, their, theirs, and themselves (or themself), as an epicene (gender-neutral) singular pronoun. It typically occurs with an unspecified antecedent, as in sentences such as:
"Somebody left their umbrella in the office. Would they please collect it?"
"The patient should be told at the outset how much they will be required to pay."
"But a journalist should not be forced to reveal their sources."
The singular they emerged by the 14th century, about a century after plural they. It has been commonly employed in everyday English ever since then, and has gained currency in official contexts. Criticism of singular they began in the late-19th century by prescriptive experts, as they deemed it to be an "error".Its continued use in modern standard English has become more common and formally accepted with the trend toward gender-neutral language, though many style guides continue to describe it as colloquial and less appropriate in formal writing.
In the early 21st century, use of singular they with known individuals has been promoted for those who do not identify as male or female.
"This is my friend, Jay. I met them at work. They are a talented artist."