Respected reference sources have signaled a modicum of acceptance of the pronoun they in a singular sense. The Associated Press Stylebook and the Chicago Manual of Style relaxed their prescriptions for singular they in recent months, allowing it in limited
circumstances. This is another step in a trend toward accepting they when referring to a single individual, usually an individual who is hypothetical, someone who is real but of indeterminate sex, or someone who doesn’t personally conform to the binary genders of male and female.
If we accept the singular they, the slippery slope argument suggests that we soon will have to accept the singular pronoun themself. If they is OK as a singular pronoun, it follows that we should at least consider themself as a reflexive pronoun:
The person who wins the prize will find themself set for life.
Themself has been used that way for hundreds of years, though it rarely appears in writing these days. If you are writing or editing in Chicago style, you have that guide’s blessing start bringing it back. AP style is not there yet.
The newest edition of the Chicago Manual of Style, just out in fall of 2017, hedges, but it says:
Themself (like yourself) may be used to signal the singular antecedent (though some people will prefer themselves) {they blamed themself [or themselves]}.
The AP Stylebook, updated for print in May 2017, doesn’t offer specific recommendation on a reflective form of singular they. In its online Ask the Editor feature, it does call themself nonstandard and suggests rewriting the sentence to avoid it.
Keep in mind that “rewrite the sentence” is the advice both style guides give when it comes to the whole issue of singular they. The new guidance simply accepts that there are some cases where it is better to go with they than to jump through hoops to avoid it.
Both style guides agree a plural verb should still be used with they when it is used as a singular, just as we use a plural verb with singular you: you are, not you is.
Linguist Neal Whitman anticipated the rising acceptance of singular they in 2010 and listed seven basic rules ready to employ once they becomes standard. The seventh is “Don’t use themselves to refer to a single individual. Instead, use themself (gasp!).” Whitman acknowledges, though, that themselves might gain more traction
The blog of Oxford Dictionaries agrees that themself is the logical form, but it says it is not yet widely accepted. Oxford advises using themselves as the singular reflective form for now.
The person who wins the prize will find themselves set for life.
The blog of Merriam-Webster Dictionaries also describes themself as the logical choice, and it points out that this form predates themselves anyway. Themselves didn’t evolve until the mid-15th century. However, Merriam-Webster says it has scant evidence for inclusion in the dictionary of this usage, concluding that “themself remains quite rare in published, edited text.”
Merriam-Webster’s dictionaries don’t include themself, and neither does Webster’s New World College Dictionary. The only American dictionaries to include an entry for themself are the online Dictionary.com, which says it is “not considered to be standard English,” and the American Heritage Dictionary, which calls it “informal.”
If you fear a future in which themself no longer raises an eyebrow, you can take heart in knowing that we are not there yet. Not quite. but the Chicago Manual of Style is ready for you to accept it (if you must), and linguists and lexicographers are no doubt keeping a close watch to see what we all decide to do.