Grammatical agreement is ignored when the usage is perceived to be politically incorrect.
Earlier authorities such as H.W. Fowler and E.B. White recommended the use of “his” in the general sense of “person” to refer to either men or women:
Everyone is expected to do his duty.
Every writer needs a room of his own.
Now, however, because this general sense of “his” to refer to a “person” of either sex is seen as exclusion of one half of humanity, the following mixed usage is common and accepted:
Everyone is expected to do their duty.
Every writer needs a room of their own.
This particular error of agreement permits speakers avoid the perceived sexism of
Everyone must do his duty.
Every writer needs a room of his own.
or the ugly awkwardness of
Everyone must do his or her duty.
Every writer needs a room of his or her own.
Writers who cannot bring themselves to mix singular and plural verbs in this way have the option of recasting such sentences all in the plural. For example,
All citizens must do their duty.
Writers need a room of their own.
NOTE: Although this mixing of singular and plural to avoid sexism is acceptable in standard English, advertisers may still wish to consider the sensitivities of the older generation of potential buyers who would be repelled by the poster headline:
“Everyone has their own ideas.”
