A clause like a major sentence, is a meaningful group of words containing a subject and predicate. However, unlike sentences, not all clauses can stand alone and make sense.

Types of Clauses

Main clause: A clause that can stand alone and make sense is known as a main clause. Every major sentence must have at least one main clause. In each of the following sentences the bold words form a main clause:

He was at the office when I arrived.
I knew why he left.
We took the train because the car broke down.

Some sentences consist of more than one main clause connected by a coordinating conjunction such as and, but or or.

Such sentences are known as compound sentences. The following sentences consist of two main clauses:

I was very angry and he knew it.
You can either apologize or you can leave immediately.
It was a sunny day but it was very cold.

The following sentences consist of more than two main clauses:

She was intelligent and she was very efficient but she had no luck in finding a job.
We can get a flight today or we can get one next week, but we cannot get one at the weekend.

Punctuation and main clauses: A comma may be used to separate main clauses joined by a coordinating conjunction, but this is not usual, especially if the clauses have the same subject and the coordinating conjunction is and.

When the coordinating conjunction is but, the use of a comma to mark off the main clause is more a matter of choice, especially when both clauses are quite long.

Subordinate Clause

A clause that cannot stand alone and make sense and is dependent on the main clause to make sense is called a subordinate clause.

A subordinate clause can come before or after a main clause. In each of the following sentences the bold words form a subordinate clause.

He arrived after we had started the meal.
He failed the exam although he worked hard.
If you buy that car you will regret it.
When he saw her he smiled.
I wonder why she left.

There are several types of subordinate clause. With the exception of a verb, a subordinate clause can replace most elements of a sentence (adverb, adjective and noun).

Noun Clause or Nominal Clause

A noun or nominal clause performs a similar function to a noun or noun phrase in a sentence. Like a noun it can act as the subject, object or complement of the main clause. The bold words in each of the following sentences are noun clauses that act as the subject of the sentence:

Where you go is of very little interest to me.
What you know should be told to the police.
What he does now is up to him.

The bold words in each of the following sentences are noun clauses that act as the object of the sentence:

I’m not asking why you’re going.
We didn’t know who had done it.
He refused to say where he was going.

The bold words in each of the following sentences are noun clauses that act as the complement of the sentence:

The theory is that there will definitely be enough money for everyone.
My point is that we simply can’t afford to move house.

Sometimes noun clauses come after a preposition. The bold words in each of the following sentences are noun clauses:

It depends on how much money is available.
They all commented on what a lot of weight he had lost.

Adverbial Clause

A subordinate adverbial clause performs a similar function to an adverb in a sentence. For example in the sentence

She left for the airport early.

The word early is an adverb. This adverb can be replaced by an adverbial clause, as in:

She left for the airport when it became light. or
She left for the airport before the city traffic got too heavy.

Relative Clause

A relative clause performs a similar function to an adjective in a sentence. It comes immediately after a noun in the main clause, which is called the antecedent, and gives more information about this noun.

A relative clause is introduced by a relative pronoun, such as who, whose, which and that, and this comes immediately after the antecedent.

Comparative Clause

A comparative clause is a subordinate clause that modifies comparative adjectives and adverbs and is introduced by than. The bold words in each of the following sentences form a comparative clause:

The task was much more difficult than any of us had anticipated.
He worked harder than we could ever have imagined.
She somehow looked less attractive today than she did last night.

Comment Clause

A comment clause is a short clause inserted into a sentence, sometimes used to show the speaker’s attitude to what he or she is saying and sometimes used as a filler without much meaning. Comment clauses are particularly common in informal speech. The bold words in each of the following sentences form a comment clause.

To put it bluntly, he is a liar.
He wasn’t sent to prison for the crime, more’s the pity.
The patient will most likely survive, I’m glad to say.
She’s only a few years older than me, you know.
He’s been married twice before, it seems.

A comment clause is often separated from the main clause by a comma.

Thanks for reading about “types of clauses in English grammar.”