
Rebecca A. answered 12/13/12
Relatable writing tutor for elementary through junior high school
Let me give you two examples to explain the correct usage of "which" and "that."
1. We recently installed new siding on our house, which was flooded last month.
Use "which" when the information in your subordinate clause ("which was flooded last month") is non-essential to the meaning of the sentence. If you took away the subordinate clause, the reader would still know what house you are referring to.
2. I returned the book that I bought last night.
You should use "that" when the information directly following it is essential to understanding the sentence. Without "that I bought last night," the reader wouldn't know which book you are talking about.
The way I remember it is by thinking of "that" as a tight knot within a sentence and "which" as a looser bow.
Jeannine E.
Excellent response, very clear and comprehensible.04/06/22

Shelly H.
I agree, but I say it differently: "Which" can be used to start a subordinate clause, but "that" is essential in the root of the sentence.04/12/22

Miss Chris S.
First and foremost, which and that are pronouns. The grammar rule: the pronoun takes the place of the noun in the independent clause: (We recently installed siding on our house) which-- takes the place of the noun-- house. was flooded last month. The pronoun-- That-- may be used but it is more informal unless it is being used as a relative pronoun to introduce a clause but not a person or people (who or whom.) There are exceptions. Yes, in restrictive and non-restrictive clauses we are concerned with using commas or not using commas according to the meaning. Example: The coat, I bought, is blue. The meaning is about the coat and not about who bought it. Therefore, the commas indicate the information is not necessary to the meaning.07/10/22
Vvvvvvvvv M.
Superb clarification. Well-put.11/01/21