"Which" introduces non-restrictive clauses:
* These clauses provide additional information about a noun that is already defined.
* They are set off by commas.
* The clause is not essential to understanding the meaning of the sentence.
Example:
* "The car, which is red, is parked outside."
* The sentence tells us there's a car. The fact that it's red is additional information.
"That" introduces restrictive clauses:
* These clauses are essential to understanding the meaning of the sentence. They define which specific noun is being referred to.
* They are not set off by commas.
* The clause is necessary for the meaning of the sentence to be clear.
Example:
* "The car that is red is parked outside."
* This sentence implies there are multiple cars, and the speaker is specifically talking about the red one.
Here's a table summarizing the key differences:
| Feature | Which | That |
|--------------|--------------------------------|---------------------------------|
| Clause type | Non-restrictive | Restrictive |
| Commas | Used | Not used |
| Necessity | Not essential to meaning | Essential to meaning |
Formal vs. Informal:
* While both "which" and "that" can be used in restrictive clauses, "that" is generally considered more formal.
* "Which" is often preferred in non-restrictive clauses, but "that" can also be used in informal writing.
In summary:
* Use "which" for non-restrictive clauses (additional information, set off by commas).
* Use "that" for restrictive clauses (essential information, no commas).
Keep in mind, there are some exceptions and stylistic preferences, so the best way to learn is through practice and reading.