คำอธิบายจาก Collins COBUILD Dictionary  

 

  he - they

        `he'

            He, him, his, and himself are sometimes used to refer back to an indefinite pronoun or to a word such as `person', `child', or `student'.

                If anybody complained about this, he was told that things would soon get back to normal.

                It won't hurt a child to have his meals at a different time.

 

            Many people object to this use because it suggests that the person referred to is male.

 

        `he or she'

            You can sometimes use he or she, him or her, his or her, or himself or herself.

                Teach a child to dial 999 and read out the telephone number from which he or she is speaking.

                The important thing is that the student should feel that that bit of writing belongs to him or her.

                Nothing excuses the child from his or her own responsibilities.

                There were several cases where one of them shot the other and then shot himself or herself.

 

            Many people avoid these expressions because they think they sound clumsy and unnatural, especially when more than one of them is used in the same sentence.

 

        `they'

            In conversation, most speakers use they, them, and their.

                Nearly everybody thinks they're middle class.

                If I think someone may attempt to take an overdose, I will spend hours talking to them.

                Don't hope to change anyone or their attitudes.

 

            This use used to be considered incorrect, but it is becoming more common in writing as well as in speech. In this book, we usually use they, them, and their.

 

            It is often possible to avoid all the above uses. You can sometimes do this by using plurals. For example, instead of saying `Every student has his own room', you can say `All the students have their own rooms'. Instead of saying `Anyone who goes inside must take off his shoes', you can say `People who go inside must take off their shoes'.