Regarding relatives: using relative pronouns

Relative pronouns are used to introduce relative clauses. Relative clauses function as adjectives in sentences, which means that they describe or give more information about a noun or pronoun. Unlike adjectives, however, relative clauses follow the noun or pronoun they modify.

There are five relative pronouns: who, whom, whose, which, and that. The first two, who and whom, are used to refer to people or animals. The last two, which and that, are used to refer to places or things. Neither should be used to refer to people. Whose, the only possessive form, may be used to refer to either.

There are two types of relative clauses: restrictive and non-restrictive.

• A relative clause is restrictive when it is necessary to identify the noun or pronoun it modifies. No commas are needed before or after a restrictive clause.

The boy who led the team onto the field is my son. [The clause 'who led the team onto the field' is necessary to identify the particular boy to whom the clause refers.]

• A relative clause is non-restrictive when the information in the clause provides extra information but is not necessary to identify the person, place, or thing it modifies. Commas are needed before and after a non-restrictive clause.

John, who led the team onto the field, is my son. [The boy is already identified by name, so the information in the clause is not necessary to identify him and is thus non-restrictive.]

Note that whether commas are used or not can actually indicate a difference in meaning of the same sentence.

The principal who sat at the head of the table proposed a toast. [Lack of commas implies that there are a number of principals sitting at the table; the clause identifies one in particular.]

The principal, who sat at the head of the table, proposed a toast. [The use of commas implies that only one principal is sitting at the table; therefore, mentioning his position at the table is not necessary to identify her or him.]

It is not vital to remember the names of the two types of relative clauses. What is important is knowing that commas are needed if the information in the clause is not necessary to identify the particular person, place, or thing the clause modifies.

In Brief: Use the relative pronouns who and whom to refer to people. Use commas before and after non-restrictive relative clauses.