Complex Relative Clauses in English

Have you ever read a sentence in English and thought: ‘This is too long and complicated’? You are probably dealing with a complex relative clause. A complex relative clause is a group of words that gives extra information about a noun. It is connected to the main sentence using a relative pronoun or adverb. These structures are very common in written English, academic texts, and formal speech.

Simple Examples to Get Started

Before we go deeper, let us look at a few basic examples to understand the idea:

The woman who called you is my sister.
The book that I bought yesterday is really interesting.
This is the city where I was born.

In each sentence, the underlined part is the relative clause. It tells us more about a noun: ‘the woman’, ‘the book’, or ‘the city’.

The Main Elements of Complex Relative Clauses in English

At an advanced level, relative clauses become more sophisticated. They can be longer, contain prepositions, or use less common pronouns. Let us explore the key components.

1. Relative Pronouns and Adverbs

The most important building blocks are the words that introduce relative clauses. Here is a quick overview:

Word	Used for	Example
who / whom	People	The scientist who discovered this is famous.
which	Things or animals	The report, which was published last year, caused debate.
that	People or things (defining only)	The idea that she proposed was brilliant.
whose	Possession	The student whose work was selected won a prize.
where	Places	The village where he grew up no longer exists.
when	Time	There are moments when silence is the best answer.
why	Reason	That is the reason why she left.

2. Defining vs. Non-Defining Relative Clauses

This is one of the most important distinctions at an advanced level.

Defining relative clauses give essential information. Without them, the sentence loses its meaning. No commas are used.
Non-defining relative clauses add extra, non-essential information. They are separated by commas.

Compare these two sentences:

The teacher who speaks Spanish is very popular. → Defining: we need this to know which teacher.
Mr. Brown, who speaks Spanish, is very popular. → Non-defining: it is just extra information about Mr. Brown.

3. Relative Clauses with Prepositions

In formal or written English, prepositions often appear before the relative pronoun. This is what makes the clause feel ‘complex’.

Informal: The project that she was working on was cancelled.
Formal: The project on which she was working was cancelled.
Informal: The person who I spoke to was very helpful.
Formal: The person to whom I spoke was very helpful.

Note that whom is used instead of who when it follows a preposition in formal contexts.

Why Complex Relative Clauses Matter

You might ask: ‘Why should I bother learning this?’ The answer is simple. These structures help you express complex ideas in a single, clear sentence. They are everywhere in English: in newspapers, academic papers, business emails, and literature. Mastering them will make your writing more precise and your reading much easier. They also make your speech sound more natural and fluent.

Comparison with Other Languages

If you speak French or Spanish, you already use relative clauses in your language. Here is a comparison to help you see the similarities and differences:

Language	Example	Notes
English	The book that I read was amazing.	Use ‘that’ or ‘which’; ‘that’ is more informal
French	Le livre que j’ai lu était incroyable.	Use ‘que’ as object, ‘qui’ as subject
Spanish	El libro que leí era increíble.	Use ‘que’ for both subject and object in most cases

One key difference: in English, you can sometimes omit the relative pronoun (‘The book I read was amazing.’). This is called a contact clause and is very common in spoken English. This does not exist in French or Spanish.

A Complete Example

Let us look at a longer sentence that combines several elements:

‘The professor whose research I admire, and to whom I wrote last month, has finally agreed to supervise my thesis.’

whose research I admire → non-defining clause using ‘whose’ to show possession
to whom I wrote last month → formal clause with preposition + ‘whom’
Both clauses are separated by commas because they are non-defining

This kind of sentence is typical in academic English. It is long, but once you understand its structure, it becomes easy to read and write.

Key Points to Remember

Relative clauses give more information about a noun in the sentence.
Use who / whom for people, which for things, and that for both (defining only).
Defining clauses have no commas. Non-defining clauses use commas.
In formal English, place the preposition before the relative pronoun: to whom, on which.
You can omit the relative pronoun when it is the object of the clause in informal English.
Practice reading academic and formal texts to see these structures in context.

Sources

Quirk, R., Greenbaum, S., Leech, G., and Svartvik, J. (1985). A Comprehensive Grammar of the English Language. Longman.
Swan, M. (2005). Practical English Usage (3rd edition). Oxford University Press.
Huddleston, R., and Pullum, G. K. (2002). The Cambridge Grammar of the English Language. Cambridge University Press.