A knotty difficulty in contemporary English usage is exemplified in a sentence that I use in my copy editing class at Loyola.
Anyone who tells you they know when this craziness will be resolved is kidding themselves.
The mixture of singular and plural pronouns and verbs has traditionally been regarded as an error in grammar. The problem is that the indefinite pronouns anyone, everyone, etc., do not have a corresponding indefinite singular objective or possessive pronoun. In English we have only his/him, hers/her and them/their. (It/its, being neuter and non-human, are ruled out.)
The ways out of the difficulty are all unsatisfactory.
The traditional remedy is to make all the pronouns masculine: Anyone who tells you he knows when this craziness will be resolved is kidding himself. But this practice, which Henry Fowler called “an arrogant demand on the part of male England,” violates the contemporary decorum of acknowledging that there are women in the human race.
The traditional remedy plus balance is ungainly: Anyone who tells you he or she knows when this craziness will be resolved is kidding himself or herself.
The modern equivocation is to take refuge in the plural: People who tell you they know when this craziness will be resolved are kidding themselves.
The gathering momentum is to accept everyone … they constructions, for which there is abundant precedent in English. R.W. Burchfield in The New Fowler’s Modern English Usage cites a passage by Samuel Johnson, and other latitudinarians recall that Jane Austen was fond of every body … their.
But though the indefinite they has become commonplace and acceptable in British usage, it remains a stench in the nostrils of American purists. That, as Bryan Garner remarks in Garner’s Modern American Usage, leaves “a happy solution elusive.”
Like the national debt, this remains a problem for our children and grandchildren to resolve.