An ELT Glossary : Clauses and Clause Elements
A sentence must have, as its minimum component, at least one main clause.
A main clause (also called an independent clause)is a group of words which create a grammatical unit which can stand alone, and which contain at least a verb. So, a single imperative verb constitutes a main clause : Stop!
Generally though, clauses will contain other units - subject, complement, object, and adverbial may or may not be present.
The following basic main clause types are found in English :
1) V : Stop!
2) V-O : Stop it!
3) V-C : Be quiet!
4) S-V-C : Anna seemed tired.
5) S-V-A : David was at the office
6) S - V (intransitive) : The dog was barking.
7) S - V - O : He liked the film
8) S - V - O - C : It made him happy
9) S - V - O - A : We put the baby to bed
10) S - V - O (indirect) - O (direct) : We gave her a book
Variations include eg the position of and number of adverbial elements in the clause, the addition of an adverbial to types 5 and 7, or the addition of an object complement to type 7. However, any variations or additional elements are always optional, whereas the clause types mentioned above are the basic grammatical patterns which are possible in English - nothing can be left out without destroying the grammaticality of the clause.
Main clauses can be joined into a single sentence by co-ordinating conjunctions :
Anna looked happy, but she seemed tired.
Be quiet and sit down!
Subordinate clauses (also called dependent clauses) cannot stand alone - they must be linked to a main clause. They must also contain a verb and may be formed by non finite verbs eg located, expecting in the following sentences :
I picked up the phone, expecting bad news.
Located next to the beach, the hotel has views of the sea from all bedrooms.
Subordinate clauses may be introduced by a relative pronoun (who/which/that, whose etc) :
That's the house which I lived in as a child.
or they may be introduced by a subordinating conjunction - eg although, because, that, while, after etc
Although I was busy, I picked up the phone.
He said that it wouldn't take long.
Relative clauses are subordinate clauses introduce by a relative pronoun such as who or which :
That's the man who I told you about.
I want one which won't break.
Subordinate clauses may also be joined by co-ordinating conjunctions :
Although I was busy and although it was late, I picked up the phone
Thus a sentence may consist of several clauses - for example, the following sentence has five :
Although I was busy and although it was late, I picked up the phone hoping that it wouldn't take long.
SC SC MC SC SC
See also : Compound and Complex Sentences