Clause

Clauses are the main structures of which SENTENCES are built. A sentence contains at least one MAIN CLAUSE. It may also contain SUBORDINATE CLAUSES. See Verb Patterns for more details on the parts of clauses.

1. Clause structure

A clause itself contains one or more clause elements.

element	examples	usual position and form
Conjunctions	and, or, if, when	a word which begins the clause (but conjunctions are always needed)
Subject	he, it, something, the bus	a pronoun or noun phrase which comes before the verb phrase
Verb phrase	like, is living, has gone	the central part of the clause, containing one or more verbs
Object (direct or indirect)	the book, Sam, People, them	a pronoun or noun phrase which follows the verb phrase
Complement	bad, very hot, a nurse, this, that	an adjective, an adjective phrase, a noun phrase, or a pronoun which follows the verb phrase and sometimes follows an object
Adverbial	away, well, at home, last night	an adverb, adverb phrase, prepositional phrase, or noun phrase which often comes after the other elements in the clause

Let's see some examples of clauses with two, three, and four elements below:

Two elements

subject (N)	verb phrase (V)
Sam	arrived.
The weather	has changed.

Three elements

subject (N)	verb phrase (V)	object (N)	complement (adj)	adverbial
Sam	likes	dogs.
James	is		very angry.
My friends	are living			not far from here.

Four elements

subject (N)	verb phrase (V)	indirect object (N1)	direct object (N2)	complement (adj)	adverbial
Sam	gave	John	a book.
Money	makes		my wife	happy.
Mr Brown	sent		us all		home.

Note: Clauses can have many different elements. For example, a clause can contain several adverbials.

2. Main clauses and subordinate clauses

One clause may be part of another clause. For example, one clause may be an object or an adverbial in another clause.
clause 1: subject + verb phrase + object (= clause 2)
Ex: I asked where the teacher lived.
→ I is a subject
→ asked is a verb phrase
→ where the teacher lived is an object and also either known as subordinate clause (adverbial) or indirect question (noun clause) where:
clause 2 (adverbial):
→ where is an adverbial
→ the teacher is a subject
→ lived is a verb phrase

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clause 1: subject + verb phrase + object + adverbial (= clause 2)
Ex: They will phone Mr Brown after they arrive.
→ They is a subject
→ will phone is a verb phrase
→ Mr Brown is an object
→ after they arrive is an adverbial also known as subordinate clause (clause 2) where:
clause 2 (adverbial):
→ after is a subordinating conjunction
→ they is a subject
→ arrive is a verb phrase

The clause (clause 1) which contains another clause is called a MAIN CLAUSE; the clause (clause 2) which is part of the main clause is called a SUBORDINATE CLAUSE.

3. Types of clause

3.1. Main clauses

Main clauses are divided into these types:

types	examples
Statements	They are lucky. | Sam's wife will be coming.
Questions	How are you? | Will Sam's wife be coming?
Imperatives	Don't be shy. | Put your gun away, please.
Exclamations	I'm so hungry! | What a surprise you gave me!

3.2. Subordinate clauses

Subordinate clauses are classified by the role they have in the main clause. For further details, see Adverbial clause, Comment clause, Comparative clause, Noun clause, and Relative clause.

But also, subordinate clauses are classified by the kind of verb phrase they contain. For further details, see Finite, Infinitive clause, Participle clause, and Verbless clause.

Note: Subordinate clauses start with subordinating conjunctions such as before, after, when, for, yet, since, nor, so, etc.

I hope this article helps. If you have any question, please leave a comment below.