Student 1, "How can we say if a given clause is a relative or adverbial?"
Student 2, "The relative clause is generally introduced by the relative pronouns 'who', 'which', 'whom', 'whose' or 'that'; whereas the relative adverb clause is using 'where', 'why' etc"
Student 1, "What is the function of a relative clause?"
Student 2, "Simple! It adds some information about the subject. This piece of information, however, is either essential and in this case, you should avoid putting the clause between commas. This is a restrictive clause. If the piece of information added does not really add any essential information about the subject of the sentence, in this case, you should put it between commas meaning that the readers are just provided some sort of explanation or reminder about the subject and that they can overlook it. This is a non-restrictive clause."
Student 1, "While writing, how I can decide if the relative clause must be restrictive or on-restrictive."
Student 2, "This is really a tough question! Let's ask the teacher!"
Student 2, "OK, Let's"
Which of the following sentences sounds accurate?
All the students who have got bad marks won't succeed.
All the students, who have got bad marks, won't succeed.
Student 1, "They look alike except for the commas, is that so?"
Student 2, "They almost look identical but the second one is completely wrong."
Student 1, "I guess it's wrong because the commas make all the students fail!"
Student 2, "Precisely, the non-restrictive clause 'who have got bad marks' is rendered optional and the commas make it additional information which we can drop and suddenly 'all the students won't succeed' what a massacre!"
Student 1, "I see, I see ... The first sentence is the correct one because the restrictive clause "no commas" limits the students who won't succeed to only those who have got bad marks."
First of all, let me give you an idea about something indispensable about the restrictive clause. Restrictive means restricting the information provided by the clause to identify the subject or the pronoun. It is also called defining clause as it defines and specifies the noun or the pronoun. It is also referred to as dependent clause because the meaning depends greatly on what comes in the clause. Did you spot the correct one among the above sentences?!
I suppose you did.
If we choose the second sentence as correct this means that all the students will not succeed; which is not logical. So it is advisable to take the first sentence for accurate because the restrictive clause -no commas- restricts and limits as well as defines the students who won't succeed : ONLY those who have got bad marks.
Take another example:
We are in the park,
The man who is wearing black glasses is an ex-army officer.
Because there are no commas in the above sentence, this means that the provided information about the subject 'the man', (who is wearing black glasses) is essential to identify the man I'm talking about. There surely are a lot of other people but our man is the only one wearing black glasses in the park. Otherwise, I'd use commas or drop the whole clause:
The man, who is wearing black glasses, is an ex-army officer.
The man is an ex-army officer.
This simply means that there is only one man in the park and the piece of information about him (wearing black glasses) is superfluous. We can omit it and the meaning is not affected.
Student 3 whispers, "Do the commas really matter?"
Student 4 answers, "Yes, they do! When the clause is between commas, this means that the information provided by the clause is optional and almost irrelevant, we can get rid of it and nothing changes!"
Student 3 "Let me see if I have that right. Now when I put the clause between commas, this means that the information it bears is not important. Is that so?"
Student 4 "Exactly, but if you omit the commas, miraculously the information becomes so important that you cannot understand the message of the utterance without it because it defines only the subject we are talking about."
Student 3 "So, the use of commas is not a game. There are places where they should be used and others where their use is a style error!"
Student 4, "Be quiet, please!"
Teacher: "The non-restrictive or non-defining clause, on the other hand, is the one you add for optional explanation and the meaning of your utterance is always valid and comprehensible even without it. It is also referred to as independent clause.
My mother, who is an excellent cook, has prepared a delicious dish for dinner.
The relative clause here is non-restrictive because it is put between two commas; which means that the information is additional and it is there just for more emphasis.
My mother has prepared a delicious dish for dinner.
As you can see the optional information is gone and the original meaning of the sentence doesn't change not like the first set of sentences.
If the meaning is not complete except with the information provided by the clause, no commas are allowed. Take this example:
The bike which my sister bought yesterday is very expensive.
The bike, which my sister bought yesterday, is very expensive.
The sentence number 1 is the accurate one. The restrictive clause is essential because it defines exactly which bike we're talking about.
The sentence number 2 is most likely to be inaccurate because the non-restrictive clause used will create some confusion. If we omit it, the sentence will become, "The bike is very expensive" which sounds incomplete as we don't really know which bike is very expensive.
The man whom the police arrested yesterday is a burglar.
The man, whom the police arrested yesterday, is a burglar
The sentence number 1 is the most accurate because the information provided by the clause is compulsory to know exactly who, among all the other men, the burglar is.
P A U S E
By the way, never use "that" with non-restrictive clauses.
Can you tell which of the following sentences are correct and justify your answer?
Monuments, which are a human heritage, must be restored.
Monuments which are a human heritage must be restored.
The boy, whom they asked to give the speech, is very shy.
The boy whom they asked to give the speech is very shy.
Your neighbour who drives a Fargo is moving to Montreal next month.
Your neighbour, who drives a Fargo, is moving to Montreal next month.
My brother, who used to study in Canada for years, came back home yesterday.
My brother who used to study in Canada for years came back home yesterday.
The house, whose balcony is falling apart, was built in the year 1925.
The house whose balcony is falling apart was built in the year 1925.