How to Use Which and That Correctly
How to Use Which and That Correctly

How to Use “Which” and “That” Correctly?

This is trickier rule involving the difference between relative pronouns “which and “that”. The proper use of “which” and “that is disregarded by people whose English is very good, but it is rule that make sense and that that’s observed by most careful speakers and writers. You are not likely to get into much trouble by neglecting this rule. To simplify  how to use which and that correctly consider the examples below:
• The car, which is parked outside, is my brother’s.
• The car that was parked outside is more expansive than this one.

Now, in the first sentence, the clause ”which is parked outside” gives us some information about the car, but it isn’t essential to the meaning of the sentence, we know the significant fact, that “the car is my brother’s” whether or not we have the additional information contained in the clause “which is parked outside.” This clause is, we can say, nonessential, or, as the grammarians put it, a nonrestrictive clause, because it gives extra information about the principal clause. We indicate its “expendable” nature by using the pronoun “which” and, in writing, by setting off the clause with commas.

In the second sentence, on the other hand, the clause beginning with “that” is clearly essential to the meaning of the sentence. Which would otherwise only tell us that one (unspecified) car is more expansive than another (unspecified) car. They are signaled by the pronoun “that,” and, in writing, they are not set off by commas.
As you can see, the rules can be pretty clearly stated: Use “which” in a nonrestrictive clause (a clause not essential to the meaning of the sentence). Use that in a restrictive clause (a clause essential to the meaning of the sentence).

Important Point:

With a restrictive clause referring to a person, you can use “that,” or, as many people prefer, “who” or “whom.” Consider the example below:

• The man that you just met is my brother-in-law. Or:
• The man whom you just met is my brother-in-law.

More examples:
• The structure which we studied yesterday was more difficult than the structure which we are studying today. (Incorrect)
• The structure that we studied yesterday was more difficult than the structure that we are studying today. (Correct)
Here’s Why: In this case “that” is correct, because the clauses are restrictive: They help us distinguish one group of structures from another group.

• The team that has lost the match is now out of the world cup. (Correct)
• The team which has lost the match is now out of the world cup. (Incorrect)
• The car, which had been stolen just an hour before, was found stripped down to its frame. (Correct)
• The car that had been stolen just an hour before was found stripped down to its frame. (Incorrect)

I hope the rules mentioned above about: “How to Use “Which” and “That” Correctly?” prove beneficial for your speaking and writing accuracy. You need to do is use it correctly so no.