Complex sentences: subordinate and relative clauses

Complex sentences let you show how ideas connect: why something happened, when, or despite what. Used well, they make your writing clearer and more mature.

Practise this lesson free (7 questions)

Main and subordinate clauses

A main clause makes sense on its own: 'We stayed inside.'
A subordinate clause adds information but cannot stand alone: 'because it was raining'.
Put them together and you have a complex sentence: 'We stayed inside because it was raining.'

Two kinds of subordinate clause

TypeStarts withExample
Adverbial clausea subordinating conjunction: because, although, when, if, since, while, unlessAlthough she was tired, Amira kept running.
Relative clausea relative pronoun: who, which, that, whoseThe girl who won the race is my cousin.

Commas and effect

If the subordinate clause comes first, put a comma after it: 'When the bell rang, everyone left.'
A relative clause that adds extra, non-essential information goes between commas: 'My brother, who hates spiders, screamed.'
Moving the subordinate clause changes the emphasis: starting with 'Although...' makes the reader wait for the main point.
Worked example

Join these with a subordinating conjunction, putting the subordinate clause first: 'The match was cancelled. The pitch was flooded.'

  1. Pick a conjunction that shows the reason: 'because' or 'since'.
  2. Put the subordinate clause first: 'Because the pitch was flooded'.
  3. Add a comma, then the main clause.

Answer: Because the pitch was flooded, the match was cancelled.

Key idea

A complex sentence has a main clause plus a subordinate clause. Adverbial clauses start with words like because, although and when; relative clauses start with who, which, that or whose. Use a comma after a subordinate clause that comes first.

Key words
Complex sentence
A sentence with a main clause and at least one subordinate clause: 'When the bell rang, we ran outside.'
Clause
A group of words with a verb and someone or something doing it. A main clause makes sense on its own; a subordinate clause does not.
Subordinate clause
A clause that does not make sense on its own: 'because it was raining'.

All KS3 English key terms and definitions →

Quick check

Try two quick questions

See if it has sunk in. Answers are marked straight away.

Extra practice

2 more questions

Try each one, then tap to check.

  1. In 'Leo kept reading although it was late', which part is the subordinate clause?

    1. Leo kept reading
    2. although it was late
    3. Leo
    4. kept reading
    Show the answer

    Answer: although it was late

    It cannot stand alone.

  2. Which word is a coordinating conjunction?

    1. because
    2. although
    3. unless
    4. and
    Show the answer

    Answer: and

    FANBOYS: for, and, nor, but, or, yet, so.

Check you have got it

Answer 7 quick questions with instant marking. If you get one wrong, GCSE-ready shows you why and gives you another go. It is free, and you do not need an account.

Practise this lesson free (7 questions)All KS3 English lessons

Video for this lesson coming soon. Subscribe on YouTube

Sources and references

Checked by the GCSE-ready editorial team, 17 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.