The structure of relative clauses must be on your checklist if you are after improving your grammar. These subordinate clauses are classified into two groups – defining (a.k.a. identifying or restrictive) and non-defining (non-identifying, non-restrictive). They enable us to omit unnecessary repetitions of a subject or an object, and sometimes even a whole sentence. Read on to learn the difference in their usage and required punctuation.

How to spot relative clauses

Relative clauses are always introduced either by relative pronouns (who and its derivatives, which, that) or by relative adverbs (when, where, why). People use them in order to present more information without composing a new sentence, as in the examples:

• I shouted at the man who trod on my foot (instead of two sentences: A man trod on my foot. I shouted at the man.)
• Lucy managed to find the corner where (or at which) the coffeehouse was situated (instead of The coffeehouse was situated at a corner. Lucy managed to find the corner.)

You should be able to spot such sentences in the process of checking your grammar in a piece of writing. Their usage stipulates for specific punctuation rules, which we will examine below.

Defining and non-defining clauses

Defining clauses convey information essential for understanding a phrase. If you cut them out, the sentence will look incomplete. Defining clauses indicate individual features of an object or a person, which you cannot detect in other objects or people of the same class. In other words, they limit all the range of objects and people to those corresponding with the criteria in defining clauses. Such clauses are never introduced by which. Moreover, they do not require any commas to separate them from the principal clause. Have a look at the examples:

• The watermelon that lies on the floor is for you. (= The watermelon lying on the floor is the only one meant for you, no matter how many other watermelons there are in the room.)
• I am planning the refurbishment of the cellar where I store my wine. (= I am planning the refurbishment of a particular cellar even if I own several of them.)

Non-defining clauses accordingly suggest that the information is irrelevant, it is only given for general knowledge and can be easily omitted. They simply describe either objects or people in question. Since such clauses contain insignificant additions, you should use commas to separate them from the principal clause. Non-defining clauses are never introduced by that in formal writings. Here are some examples:

• Julia, who was only 14 when I first laid my eyes on her, has turned into a beautiful miss. (If you cross out the relative clause, you will get a perfectly structured sentence, which means the clause is non-defining.)
• When I drove past the neglected school, where I used to spend the days of my childhood, I noticed a girl in a silk dress. (Now we will convert it into a defining clause so that you surely get the hang of it: I drove past the neglected school where I used to spend the days of my childhood.)

These distinctions give you certain freedom in expressing yourself. When you write a paper, you are the one to decide what clauses are relevant for the meaning and what clauses sound better when separated by commas, and then you can build your sentence correspondingly. It is the pronouns that may present difficulties in the course of mastering relative clauses. The general rule in academic English is that that goes without commas (and is used in defining clauses), while which always requires them (and is used in non-defining ones).

Tips and nuances

1. When you refer to a person, you had better choose the pronoun who, although that can be also used in informal style to draw attention to people’s skills or unique features:

• These volleyball girls that/who serve the ball so brilliantly will win a championship one day.
• Tim is the kind of friend that/who is not afraid of pointing out your drawbacks.

1. You should prefer that to which when putting a relative clause after a superlative adjective or such words as none, nothing, something, all, everything etc.

• It is the best painting that has ever existed!
• A bit of quiet is all that I ask for.

1. If your focus is on a person or a thing functioning in the sentence as an object, you can skip the relative pronoun (that, who, whom, which). Such omission is not preferable in official English but is perfect for everyday communication.

• When was delivered the cake (that) I had asked for?
• I got you an autograph of the rock star (who) you adore.

1. When a relative pronoun is used with a preposition, then you should use which instead of that, like in next combinations: about which, for which, along which, in which etc. Despite the grammatical correctness of the given constructions, employing other suitable pronouns (such as where and why) may sound more natural here:

• Look at the room in which (where) he stayed overnight.
• Do you know the reason for which (why) I gave up my music band?

1. Whom sounds bookish and official, which probably will not suit your purpose. Substitute it for who or omit the preposition at all:

• The librarian to whom I spoke was extremely polite. → The librarian (who) I spoke to was extremely polite.

However, you cannot omit whom when it is preceded by a preposition:

• The delivery man for whom Ann had been waiting the whole morning finally arrived.

1. Whose can refer to both objects and people. It is the only possessive relative pronoun the English language has.

• Please meet Joey whose father is a hereditary doctor.
• The magazine whose editor in chief is an eccentric woman gains popularity.

We believe that mastering English relative clauses is just a matter of time and effort. This grammar issue has its own peculiarities, as every other aspect does. You should remember two main types of relative clauses – defining and non-defining – and the crucial distinctive feature each of them has, which is the extent of their significance in the sentence structure. But no matter what happens, Royal Editing staff will support you in your academic initiatives and make sure that your papers are free of any mistakes, including those in relative clauses.