We use who and whom for people, and which for things.
Or we can use that for people or things.
We use relative pronouns:
• after a noun, to make it clear which person or thing we are talking about:
the house that Jack built
the woman who discovered radium
an eight-year-old boy who attempted to rob a sweet shop
• to tell us more about a person or thing:
My mother, who was born overseas, has always been a great traveller.
Lord Thompson, who is 76, has just retired.
We had fish and chips, which is my favourite meal.
But we do not use that as a subject in this kind of relative clause.
We use whose as the possessive form of who:
This is George, whose brother went to school with me.
We sometimes use whom as the object of a verb or preposition:
This is George, whom you met at our house last year.
This is George’s brother, with whom I went to school.
But nowadays we normally use who:
This is George, who you met at our house last year.
This is George’s brother, who I went to school with.
When whom or which have a preposition the preposition can come at the beginning of the clause…
I had an uncle in Germany, from who[m] I inherited a bit of money.
We bought a chainsaw, with which we cut up all the wood.
… or at the end of the clause:
I had an uncle in Germany who[m] I inherited a bit of money from.
We bought a chainsaw, which we cut all the wood up with.
We can use that at the beginning of the clause:
I had an uncle in Germany that I inherited a bit of money from.
We bought a chainsaw that we cut all the wood up with.
Which or That?
While both which and that can be used in other constructions, the confusion usually arises when they are being used as relative pronouns to introduce adjective (or relative) clauses. In the examples below, we have bracketed the adjective clauses. (Remember that a clause is simply a group of words containing a subject and a verb):
1. Our house [that has a red door and green shutters] needs painting.
2. Our house, [which has a red door and green shutters], needs painting.
3. The classrooms [that were painted over the summer] are bright and cheerful.
4. The classrooms, [which were painted over the summer], are bright and cheerful.
In all four cases, the adjective clause tells us something about either the house or the classrooms, but the choice of which or that changes the way we should read each sentence.
In the first sentence, the use of that suggests that we own more than one house and therefore must explain to you that we are talking about a particular house of ours–the one with a red door and green shutters. We cannot leave out that adjective clause because it is essential to your understanding of the sentence; that is, you wouldn’t know which one of our houses needs the paint job without that adjective clause.
The second sentence tells you that we own only one house and we are simply telling you–in case you want to know–that it happens to have a red door and green shutters. We could leave out the information in that adjective clause and the sentence would still make sense.
The third sentence, because it uses that to launch its adjective clause, tells us that only SOME of the classrooms were painted over the summer. If we omitted the clause “that were painted over the summer,” we would be left with “The classrooms are bright and cheerful,” a statement that would not be accurate since it would imply that ALL the classrooms are bright and cheerful. In this sentence, therefore, the adjective clause is essential to the meaning of the sentence.
We call the adjective clauses in sentences one and threerestrictive because they restrict–or limit–the meaning of the nouns they modify. In the case of sentence three, they tell us that we are talking ONLY about the classrooms that were painted over the summer–not the others.
The which clause in the fourth sentence is what we call a nonessential–or nonrestrictive–clause. Since that sentence intends to tell us that ALL the classrooms were painted, the information in the adjective clause is not essential. The sentence would be clear even if the clause were omitted.
The rule of thumb, then, is that which clauses are nonrestrictive (nonessential) while that clauses are restrictive (essential). Nonrestrictive clauses and phrases are set off from the rest of a sentence by a pair of commas (as in our examples above) or by a single comma if they come at the end of the sentence. (Example: “I took a vacation day on my birthday, which happened to fall on a Monday this year.”)
Merriam-Webster’s Collegiate Dictionary (10th edition), regarded by most writers as the authority on such matters, tells us that it is now common for which to be used with either kind of clause, while that must be used only for restrictive clauses. In fact, though, careful writers continue to make the distinction we describe above. Attorneys are taught to use which for nonrestrictive clauses and that for restrictive clauses so as not to cause a misreading in legal documents. It seems just as important that we work to avoid misreadings in all writing, not only in situations when a legal ruling might be at stake.
source : British council and get it write
I.Which pronoun–which or that–belongs in each blank below?
1. Carlos gave Maria a study guide for material ________ was going to be on the test.
2. Carlos gave Maria notes from chapters 3 through 7 _________ were going to be on the test.
3. Mark and Sarah took their children on every vacation _________ they took to the coast.
4. The teachers gave awards to all paintings ________ showed originality.
1.Carlos gave Maria a study guide for material *that* was going to be on the test. [To say simply “Carlos gave Maria a study guide for material” would not be complete information. We need the adjective clause to tell us which material, in particular. Since the information is, therefore, essential, we use that and no comma.]
2.Carlos gave Maria notes from chapters 3 through 7, *which* were going to be on the test. [The fact that chapters 3 through 7 were going to be on the test is not essential to our understanding exactly which notes Carlos gave Maria, so we use a comma and which.]
3.Mark and Sarah took their children on every vacation *that* they took to the coast. [If we said simply “Mark and Sarah took their children on every vacation,” we would be inaccurate. The information in the adjective clause is essential to our understanding that the children went on certain vacations and not others. Therefore, we use that and no comma.]
4.The teachers gave awards to all paintings that showed originality. [To say simply “The teachers gave awards to all paintings” would be inaccurate. The information in the adjective clause is, therefore, essential to the meaning of the sentence, so we use that and no comma.]
II.Choose the best answer.