Confusion over the use of which and that is not something that you should be ashamed of. These two words are often misused even by writers. This post will shed light on when and how to use these terms.
Generally, that can be used in clauses referring to people, groups, or things.
“Search on for man that robbed Fall River gas station with gun”
Fall River Herald News
“The Study That Said Female Doctors Are Better Than Male Doctors”
“Five factors that are likely to chart market direction this coming week”
Meanwhile, which can only be used in clauses that refer to groups or things.
“US states propose new laws which could stop people protesting against Donald Trump”
“Police make arrests 23 years after LA fire which killed 10”
“Romanian government to repeal law which decriminalises corruption”
Also, that is used to introduce essential or restrictive clauses. These are relative clauses that limit a general, ambiguous noun and enable the reader to determine which one the writer is referring to. These clauses add information that is critical to the sentence’s message.
“The FBI Is Building A National Watchlist That Gives Companies Real Time Updates On Employees”
“The Hawaiian volcano that created a spectacular firehose of lava just collapsed”
“Love Wins In 2017: Here Are 25+ Valentine’s Day Gifts That Give Back”
On the other hand, which is used to introduce nonessential or nonrestrictive clauses. These clauses only add supplementary information.
“Tell us your fondest Falcons memories, which will hopefully be replaced soon”
“Hitler’s phone, ‘which sent millions to their deaths,’ to be sold at auction”
“Bargain hunters swarm library book sale, which continues through Sunday”
Glens Falls Post-Star
Notice that if you try to remove the essential clauses, it will completely change the meaning of the sentence while nonessential clauses can be removed without completely affecting the meaning. Remember that essential clauses are not are not preceded or surrounded by commas while nonessential clauses are always introduced or surrounded by commas.