Catherine Soanes asks: Is ‘themself’ a real word? She says, “Judging by the debate on the Net, themself stirs up much passion, with several pundits confidently declaring that ‘themself is not a word’. Well, much as I hate to be the bearer of bad news, themself is a word and it has a long history to boot.” That history is quite interesting:
The Oxford English Dictionary (OED) records themself from the 14th century. It doesn’t have a separate entry of its own, but a note at the entry for themselves informs us:
in standard English themself was the normal form to c1540, but disappeared c1570. Themselfs, themselves appears c1500, and became the standard form c1540.
So for around 150 years, themself (though ending with the singular suffix –self) was considered to be correct when used to refer to a plural subject. A little more OED-delving shows that a similar situation existed when it came to first person plural reflexive pronouns. The form ourself is first recorded in the 14th century, when it was an accepted usage. There must have been a move towards pluralizing the singular suffix –self to –selfs or –selves for plural reflexive pronouns in the early to mid 16th century, when the forms ourselves and themselves first appeared.
Returning to the OED note, themselfs (with only 26 examples on the OEC) is no longer acceptable and has largely dropped out of use, meaning that for almost 500 years the main standard reflexive pronoun which corresponds to the plural forms they and them is the plural form themselves […].
She winds up with this sensible recommendation:
Given that it’s now largely acceptable to use they, them, or their instead of the more long-winded ‘he or she’, ‘him or her’, or ‘his or her’ (especially in conjunction with indefinite pronouns such as anyone or somebody) it might be argued that, logically, it should also be OK to use themself, it being viewed as the corresponding singular form of themselves. However, this isn’t yet the case, so beware of themself for now!
I myself occasionally use themself; it sounds a little strange, but I feel I’m helping advance the shining future.