Which or That?

Charlottesville

November 13, 2026

I must have missed this day in seventh grade grammar class. Glad to know I can 55 years later start to use the words correctly!

Why did the grammar book break up with the style guide?

Because it couldn't tell the difference between a clause that restricts the meaning and a clause which, by the way, just likes to hang out with extra commas.

The main difference between that and which is whether the clause they introduce is essential (restrictive) or non-essential (non-restrictive) to the meaning of the sentence.

• That (Essential / Restrictive): Introduces information required to identify the noun or understand the core sentence. If you remove the clause, the sentence's meaning changes or becomes incomplete. Do not use commas with that.

• Example: "The car that has a flat tire is mine." (Tells us which specific car we mean out of many).

• Which (Non-Essential / Non-Restrictive): Introduces extra, bonus information that can be removed without changing the main point of the sentence. Always set off which clauses with commas.

• Example: "My car, which has a flat tire, is in the driveway." (We already know which car it is; the flat tire is just extra detail).

Quick Test

• The Deletion Test: Try removing the clause. If the sentence still makes sense and points to the exact same thing, use which (with commas). If the sentence loses crucial meaning or becomes ambiguous, use that (without commas).