That or Which?
Have you ever found yourself lost because you could not decide whether to use “which” or “that” in a sentence? I did! But not anymore! I would like to present some rules, as found in the book ”The Elements of Style” by Strunk and White.
“That” is defining, restrictive, limiting. Use it to specify which one. You cannot split the sentence into two without losing information.
“Which” is nonrestrictive, non-defining. Use it to add a fact about the noun to the text. You could split the sentence into two. Note that nonrestrictive relative clauses are parenthetic; comas are therefore needed.
In many sentences either one can be employed, but the sentence’s meaning is changed.
Example A
“The neighbor’s dog, which I killed yesterday, was purple.”
means “The neighbor’s dog was purple. And also I killed the neighbor’s dog yesterday.”
“The neighbor’s dog that I killed yesterday was purple”
means “Yesterday I killed the neighbor’s purple dog.” They have more than one dog and I killed the purple one. It cannot be split into two sentences: “The neighbor’s dog was purple. Yesterday I killed the neighbor’s dog.” In the second sentence, information about which of the neighbor’s dogs I killed is missing.
Example B
“We were donated 8 sequences that comprise between 500 and 1500 frames.” Wrong. It can be split into two sentences: “We were donated 8 sequences. The 8 sequences comprise between 500 and 1500 frames.” Furthermore, “comprise between 500 and 1500 frames” does not define which sequences we were donated. One cannot ask: ”Which 8 sequences?” Answer: “The ones that comprise between 500 and 1500 frames.“ Correct: “We were donated 8 sequences, which comprise between 500 and 1500 frame.”
Example C
“The set K contains only numbers, which are larger than k“. Wrong, unless the author wanted to say “The set K contains only numbers.” and “In the set K, all numbers are larger than k.” “Which are larger than k” is not meant to add a fact about K, but to define K. Correct: “The set K contains only numbers that are larger than k.”
This should help careful writers improve their work.
grammar, this, which