What does a relative pronoun do?
Within the subordinate clause the relative pronoun may act as subject or object. Trust no man who does not love his country. (Here the relative pronoun who acts as the subject of the clause who does not love his country.) There I met an old man whom my father had known. (Here the relative pronoun whom acts as the object of the clause whom my father had known.) Note that a relative pronoun used as an object will be followed by another noun. In the example given above my father is the subject of the relative clause ‘whom my father had known’.
