Which or That?

[Han26+]

When is the use of “which” correct, and when is the use of “that” correct? I’ve an inkling they are not interchangeable.

[Fazzier]

I've always used 'which' and 'that' interchangeably. Do they have any difference?

[EvaDar]

This question has to do with restrictive and non-restrictive clauses. The following link is good as it addresses British and American styles. Basically, if the clause contains essential information (restrictive), that would be used. If non-essential (non-restrictive), then which is used. With which, a comma is usually needed.

The backpack that was found on the bus was red.
The clause that contains that is essential. If you remove the clause, the meaning of the sentence is not conveyed correctly.
The backpack was red.
The sentence is still grammatically correct, but it is not enough information. It is essential (restrictive) information that the backpack was found on the bus. Both elements are important and tell us that it was a red backpack that was found on the bus.

The backpack, which is red, was found on the bus.
This tells us a back pack was found on the bus, and the fact that it is red is additional information. The point is it was left on the bus. You can remove the which clause and the sentence still conveys the information correctly (non-restrictive).
The backpack was found on the bus.

This link has more detail:
https://en.oxforddictionaries.com/usage/that-or-which

[Dawud Adaviruku]

This question has to do with restrictive and non-restrictive clauses. The following link is good as it addresses British and American styles. Basically, if the clause contains essential information (restrictive), that would be used. If non-essential (non-restrictive), then which is used. With which, a comma is usually needed.

The backpack that was found on the bus was red.
The clause that contains that is essential. If you remove the clause, the meaning of the sentence is not conveyed correctly.
The backpack was red.
The sentence is still grammatically correct, but it is not enough information. It is essential (restrictive) information that the backpack was found on the bus. Both elements are important and tell us that it was a red backpack that was found on the bus.

The backpack, which is red, was found on the bus.
This tells us a back pack was found on the bus, and the fact that it is red is additional information. The point is it was left on the bus. You can remove the which clause and the sentence still conveys the information correctly (non-restrictive).
The backpack was found on the bus.

This link has more detail:
https://en.oxforddictionaries.com/usage/that-or-which

Thank you for sharing this detailed explanations. It's great.

[Renu G]

This is very helpful. Thank you very much. I think one can get a doctorate in English grammar by becoming a good reviewer for OBC!

[roxy60sweet]

'That' should always precede a restrictive or defining clause. 'Which' should always precede a non-restrictive or nondefining clause and be preceded by a comma.

[Bukari]

Thanks for the clarification, but the inclusion of a comma after "which" is still controversial among most editors.

[Agnes Masobeng]

This question has to do with restrictive and non-restrictive clauses. The following link is good as it addresses British and American styles. Basically, if the clause contains essential information (restrictive), that would be used. If non-essential (non-restrictive), then which is used. With which, a comma is usually needed.
The backpack that was found on the bus was red.
The clause that contains that is essential. If you remove the clause, the meaning of the sentence is not conveyed correctly.
The backpack was red.
The sentence is still grammatically correct, but it is not enough information. It is essential (restrictive) information that the backpack was found on the bus. Both elements are important and tell us that it was a red backpack that was found on the bus.

The backpack, which is red, was found on the bus.
This tells us a back pack was found on the bus, and the fact that it is red is additional information. The point is it was left on the bus. You can remove the which clause and the sentence still conveys the information correctly (non-restrictive).
The backpack was found on the bus.

This link has more detail:
https://en.oxforddictionaries.com/usage/that-or-which

The link you provided is even more helpful. It has a lot of helpful information, thank you.

[EvaDar]

The link you provided is even more helpful. It has a lot of helpful information, thank you.