Complex Sentences

A complex sentence joins a main clause (a complete idea that can stand alone) with one or more subordinate clauses (ideas that depend on the main clause to make sense). At this level, you will focus on two powerful types of subordinate clause: relative clauses and adverbial clauses.

What You'll Learn

In P4, you learned to combine a main clause with a subordinate clause using common conjunctions like "because" and "when". Now in P5, you will go further:

Build relative clauses using the pronouns who, which, that, whose, and where to add detail to a noun
Construct adverbial clauses of time to explain when something happens
Construct adverbial clauses of reason to explain why something happens
Construct adverbial clauses of contrast to show an unexpected or opposing idea

When to Use

Adding information about a person: "The scientist who discovered the vaccine received an award." (The relative clause tells us which scientist.)
Adding information about a thing or animal: "The report that was published last week surprised many readers." (The relative clause identifies which report.)
Showing when something happened: "After the ceremony ended, the students gathered at the canteen for refreshments." (The adverbial clause of time tells us when.)
Explaining a reason: "The outdoor lesson was cancelled because the haze conditions worsened overnight." (The adverbial clause of reason tells us why.)
Expressing contrast or surprise: "Although the team had practised for months, they did not win the competition." (The adverbial clause of contrast shows something unexpected.)

How to Form

Relative Clauses

A relative clause begins with a relative pronoun and comes right after the noun it describes.

Relative Pronoun	Used For	Example
who	People	The teacher who taught us Science has retired.
which	Things / Animals	The novel which I borrowed from the library was fascinating.
that	People / Things (informal)	The parcel that arrived this morning is for you.
whose	Possession	The boy whose bicycle was stolen reported it to the police.
where	Places	The hawker centre where we usually eat is being renovated.

Structure: Noun + relative pronoun + rest of the clause + main clause continues

"The girl who sits beside me is from Penang." Main clause: The girl ... is from Penang. Relative clause: who sits beside me (adds detail about "the girl")

Adverbial Clauses

An adverbial clause acts like an adverb -- it tells us when, why, or introduces a contrasting idea. It is joined to the main clause by a subordinating conjunction.

Type	Conjunctions	Example
Time	when, while, before, after, until, as soon as, since	Before the bell rang, the pupils had already lined up.
Reason	because, since, as	She excelled in the examination because she revised every day.
Contrast	although, even though, though, while	Even though it was raining heavily, the runners continued the race.

Two positions for adverbial clauses:

Position	Punctuation	Example
Before the main clause	Comma after the adverbial clause	Although he was exhausted, he finished the project.
After the main clause	Usually no comma needed	He finished the project although he was exhausted.

Key Rules

Place relative clauses immediately after the noun they describe: Do not separate the noun from its relative clause with other words. Write "The book that I read was exciting," not "The book was exciting that I read."
Use "who" for people and "which" for things: While "that" can replace either in informal writing, exam questions usually expect "who" for people and "which" for things. "The woman who lives next door is a pilot." "The MRT line which opened last year is very convenient."
"Whose" shows possession: It replaces "his", "her", "its", or "their" inside the clause. "I know the student. Her essay won the prize." becomes "I know the student whose essay won the prize."
Use a comma when an adverbial clause comes first: When the subordinate clause appears before the main clause, follow it with a comma. "After the guests left, we cleaned the hall." No comma is needed when the main clause comes first: "We cleaned the hall after the guests left."
Do not use "although" and "but" in the same sentence: These both signal contrast, so using both is redundant. Write "Although it rained, we went out," or "It rained, but we went out" -- not "Although it rained, but we went out."
A subordinate clause cannot stand alone: "Because I was tired" is not a sentence by itself. It must be attached to a main clause: "Because I was tired, I went to bed early."

Common Mistakes

Wrong	Right	Why
The boy which won the race is my classmate.	The boy who won the race is my classmate.	Use "who" for people, not "which".
The book who I borrowed was interesting.	The book which I borrowed was interesting.	Use "which" (or "that") for things, not "who".
Although she studied hard, but she failed.	Although she studied hard, she failed.	Do not pair "although" with "but". Choose one.
Because I was late. The teacher scolded me.	Because I was late, the teacher scolded me.	A subordinate clause cannot be a sentence on its own. Join it to the main clause.
The girl is my neighbour who wears glasses.	The girl who wears glasses is my neighbour.	The relative clause must sit right after the noun it describes ("the girl").
The shop where that sells roti prata is closed.	The shop that sells roti prata is closed.	Do not combine "where" and "that". Use "that" when describing what the shop does, and "where" when describing a location (e.g., "the shop where we buy roti prata").

Clue Words

Relative clause signals

who, which, that, whose, where, whom

Time clause signals

when, while, before, after, until, as soon as, since, once

Reason clause signals

because, since, as

Contrast clause signals

although, even though, though, while, whereas

Tip: If you can ask "which one?" about a noun in the sentence, you may need a relative clause. If you can ask "when?", "why?", or "but what?", you may need an adverbial clause.

Practice Tips

The "which one?" test for relative clauses: After reading a sentence, point to the noun and ask "Which one?" If the answer is missing, a relative clause can provide it. "The student received a trophy." -- Which student? "The student who scored the highest received a trophy."
The "stand-alone" test for subordinate clauses: Cover the main clause and read only the subordinate clause. If it sounds incomplete on its own, you have correctly identified it as a dependent clause that needs a main clause.
The "move it" test for adverbial clauses: Try moving the adverbial clause to the other end of the sentence. If the meaning stays the same and you adjust the comma correctly, you have identified the clause correctly. "After dinner, we played chess." can become "We played chess after dinner."
The "although vs but" check: Scan your sentence for both "although" (or "even though" / "though") and "but". If you see both, delete one. Keep whichever one makes the sentence sound more natural.

Quick Reference

Clause Type	Starts With	Purpose	Example
Relative (people)	who, whose, whom	Describes a person	The nurse who treated me was kind.
Relative (things)	which, that	Describes a thing or animal	The cake which she baked was delicious.
Relative (places)	where	Describes a place	The park where we jog has a new playground.
Relative (possession)	whose	Shows ownership	The author whose book I read is visiting our school.
Adverbial (time)	when, before, after, while, until, as soon as	Tells when	When the rain stopped, we went outside.
Adverbial (reason)	because, since, as	Tells why	He was late because the bus broke down.
Adverbial (contrast)	although, even though, though, while	Shows surprise or opposition	Although she is young, she speaks three languages.

Complex Sentences (P5) (Primary 5)