- I drove 1400 miles by myself.
- He walked there by himself.
- She accomplished the feat by herself.
These all seem straightforward enough. But what about when you are writing about someone whose gender is unspecified, and in a sentence where clearly the pronoun 'one' does not apply?
- The self-aware individual perceives themself.
While both 'theirself' and 'themself' are sometimes used in this situation, neither one is recognized as correctly spelled by word processors or is listed in modern dictionaries. At first glance it may seem that both are worthy candidates for this role. However - in my opinion - theirself is far more accurate. I am not entirely certain, but I think it sounds more correct to me because 'their' is sometimes used in a singular context whereas 'them' is not. For example:
- The person was eating their dinner.
- The child was doing their homework.
While it could be argued that the acceptance of 'themselves' as well as 'theirselves' means that 'themself' is just as valid as 'theirself', to me 'themself' is nothing more than an awkward monstrosity due to its juxtaposition of something undeniably plural (them) with something almost-always singular (self).
English - however - is extremely flexible, so in the end each person will have to decide for theirself which is correct.
Update [Sept 2019]: Merriam-Webster has added singular 'they,' 'theirself,' and also 'themself' to their dictionary: