In these sentences, who and which and what are the interrogative pronouns, used to ask questions concerning the unknown persons or objects.

230. Who refers only to human beings or to personified objects.

Which refers either to human beings, animals or things.

What refers only to things.

Which and what have the same form for both the subject and the object. Who has a different form for all three forms, the subject form, the possessive form, and the object form. It uses the same form, however, both in singular and plural.

Subject formPossessive formObject form
WhoWhoseWhom

231. We often make mistakes in the use of the different forms of the pronoun who. We often use the subject form for the object form, using who where we should have used whom. For example:

The correct form is: