That, Which, Who, Whom, and Whose

Many people appear to be confused over whether to use that or which in certain constructions. Ms. Picky will be happy to explain. 

That and which belong to a class of words known as relative pronouns, which also includes who, whom, and whose. These words are pronouns, because they take the place of a noun (e.g., “he” or “she” for persons, or “it” for things), but they are relative pronouns when they relate, or refer, to another word in the sentence.

Example:

A. He is the man who committed the felony.

(“Man” is a noun, and it is the antecedent of “who.” “Who” relates to man; hence it is a relative pronoun.)

B. The Economist, which is her favorite magazine, is a weekly publication.

(“Economist” is a noun and the antecedent of “which.” “Which” relates to Economist; hence it is a relative pronoun.)

In order to choose the correct relative pronoun, one must ask two questions:

1. Is the relative pronoun’s antecedent a person or a thing?

2. Is the clause with the relative pronoun restrictive or nonrestrictive?

Question 1: Is the Relative Pronoun's Antecedent a Person or Thing?

•      The relative pronouns who, whom, and whose refer to persons. 
•      The relative pronoun which refers to things.
•      The relative pronoun that can refer to people or things.

In example A, above, “man” is a person, not a thing, and therefore takes a personal pronoun—in this case, who.

In example B, above, “Economist” is a thing, not a person, and therefore takes a relative pronoun used for things—in this case, which.

Question 2: Is the Meaning of the Clause Restrictive or Nonrestrictive?

“Restrictive” and “nonrestrictive” are terms that sound more complicated than they are. Ms. Picky will explain. (The same distinction applies to both “person references” and “thing references.”) Let’s look at some examples. 

Restrictives

Example of a Restrictive Reference to a Person: The girl who is dressed in blue is my daughter. “Who is dressed in blue” restricts the word “daughter” to mean only the girl dressed in blue—not any other girls who happen to be standing nearby, who might be dressed in green or lavender.

Example of a Restrictive Reference to a Thing: This is the book that I wanted to buy. “That I wanted to buy” is used to restrict the understanding of the word “book” to mean only the book I wanted to buy—not any of the other 18,617 books in the shop.

Commas are not used with restrictives, because the relative pronoun is so closely allied with its antecedent that it is essential to the meaning of the rest of the sentence and must not be separated from it in any way.

Nonrestrictives

Example of a Nonrestrictive Reference to a Person: Her son, who is such a sweet young man, is going to take a year off from his studies to travel. “Who is such a sweet young man” is extraneous information, an “aside” that is unnecessary to the essential information being conveyed. (Think of nonrestrictives as kind of a “by-the-way”addition—interesting perhaps, but not essential.)

Example of a Nonrestrictive Reference to a Thing: The volume you selected includes “The Pit and the Pendulum,” which has always been a favorite of mine.  In this case, the clause “which has always been a favorite of mine” is nonrestrictive. It gives extra, nonessential, or parenthetical, information.  (If you’ve already selected the book, you don't really need to know if it’s someone else’s favorite or not.)

Commas are used with nonrestrictives, because the information in the nonrestrictive clause is separate and apart from the essential meaning of the sentence, and commas indicate its separateness.

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Bottom Line

•     Which is used to connect a clause that adds extraneous, nonessential information about a thing or things. It is always used with commas.
•     That connects a clause that restricts the meaning of its antecedent to a particular person or thing. It is always used without commas.
•     Who, whom, or whose is used to connect either a restrictive or nonrestrictive clause, but is always used to relate to a person. Used in a clause with commas, who, whom, or whose is used to add extraneous, nonessential information about a person or persons; used in a clause without commas, it restricts the meaning of its antecedent to a particular person or persons.