English has no sex-neutral third person singular pronoun (ie one that expresses the common meaning of he and she), and so the plural pronoun they is often used informally (especially in BrE), in defiance of number concord, as a substitute for the indefinite pronouns everyone, everybody, someone, somebody, anyone, anybody, no one, nobody.
Everyone thinks they have the answer [42]
Has anybody brought their camera? [43]
No one could have blamed themselves for that [44]
The plural pronoun is a convenient means of avoiding the dilemma of whether to use the he or she form. The same dilemma can arise with coordinate subjects and with some indefinite noun phrase subjects, but here, resort to the evasive device of the plural pronoun is perhaps not so acceptable:
? Either he or his wife is going to have to change their attitude
? Not every drug addict can solve their problem so easily
The use of they in sentences like [42-44] is frowned upon in formal English, where the tendency is to use he as the 'unmarked' form when the sex of the antecedent is not determined. The formal equivalent of [42] is therefore:
Everyone thinks he has the answer [42a]
The same choice is made in referring back to a singular noun phrase with a personal noun of indeterminate gender as head:
Every student has to make up his own mind [45]
Although this use of he often sounds pedantic, there is no obvious alternative to it, in formal English, except the rather cumbersome device of conjoining both male and
female pronouns:
Every student has to make up his or her own mind [45a]