Usage of ‘that’ and ‘which’ often causes confusion. Why so? Go through the rule that differentiates the two:

That: That should be used to introduce a restrictive clause.
Which: Which should be used to introduce a non-restrictive or parenthetical clause?

Easy-peas right? Well, not quite. Let’s break it down and make it into something which is easier for you to digest.

Definition of a restrictive clause: A restrictive clause is an element of the sentence that cannot be deleted because it restricts the noun. For example, Issues that concern minorities cannot be ignored.

If a restrictive clause could not be left out of the sentence, a non-restrictive clause is its exact opposite and can be left out without changing the meaning of a sentence. Non-restrictive clauses are either in brackets or have a comma before and after them (or only before them if they come at the end of a sentence).

In both the sentences above, the fragment in ‘bold’ can be easily left.

In essence, if you can remove ‘which’ from a sentence and the meaning of the sentence is not harmed, that sentence will take a ‘which’ only. In case the meaning is harmed without the ‘that’ fragment, you need to use ‘that’.