That vs. Which

The rules of restrictive versus non-restrictive, which govern the decision in selecting a relative pronoun in a sentence, can be applied to all cases of comma usage in the English (US) language's grammar rule on commas, including the Oxford and parenthetic clauses, which inherently dictates the assignment of open form and closed form styles, previously undefined.

Understanding That

Use that to indicate that the fragment that follows the pronoun limits, or “restricts,” the referenced object with the information that follows.

In the case of the use of that as a restrictive pronoun, a comma does not precede the pronoun or set off the clause.

For example:

The color that I chose is my favorite.

- In this example, I am specifying that my favorite color is the one I chose.

Which One That?

To simplify this complicated rule, the question of knowing if there is only one subject or more than one subject being modified by one of the relative pronouns (that or which) is offered as follows:

Do I already know which one?

If no further detail is needed to identify the target subject of the relative pronoun based on the context provided up to that point, then no further clarification is necessary to the audience.

For example:

The cat that I saw…

{The text after the word that is provided to clarify to the audience that, while there may be many cats, only the one that I saw is the subject being modified.}

The cat, which I saw,…

{The one cat that is the subject being modified is already clearly identified by the audience.}

Deciding Which One

Use which to indicate that the fragment that follows is supplemental in nature and does not further define or restrict the referenced object. In the case of the use of which as a non-restrictive pronoun, a comma precedes the pronoun and sets off the clause if the sentence continues passed the non-restrictive clause.

For example:

The color, which I chose, is my favorite.

- In this example, the color is my favorite, and I chose it. It is implied that the reader knows which color is being referenced; however, for the sake of clarity, this sentence can add the referenced color “red,” whereas the previous sentence would be awkward if the color is clearly defined.

Awkward: “The color red that I chose...” Since that is a restrictive pronoun, an identifying attribute (in this case, red) is not necessary and confuses the reader in the above context, because the parenthetic clause that follows serves to further define the referenced object. In this case, there would have to be different shades of red being referenced in order for this sentence to make sense and avoid sounding awkward. If there was only one available “red” as reference, then the reader should find this sentence awkward.

Implied: “The color red, which I chose,...” Since which is a non-restrictive pronoun, the parenthetic clause does not further define the referenced object, because the reader knows what is being referenced.

Other pronouns, such as who, are determined to be restrictive or non-restrictive based on the use of the comma.

For example:

“The person who shall remain nameless...”

- In this case, you are identifying a specific person from among a group of people as the one who will not be named whereas the others might be named.

“The person, who shall remain nameless,...”

- In this case, you know which specific person has been identified already and are further stating that the specific person will not be named throughout the remainder of the discussion. Also, there is no indication if the person is alone or within a group.

See Appositives for more information.

This has been a Chen Dushek public knowledgeshare--very rare