Clause

A clause is a part of a sentence. Each clause is made up of a subject (who or what the sentence is about) and a predicate (what happens in a sentence). Each predicate has only one main verb.

I love you is a sentence that has only one clause. I love you and I will always love you is a sentence that has two clauses: I love you and I will always love you. Both clauses are joined together by the word and, which is a conjunction. Clauses may be independent or dependent.

 In use 
Two clauses can be joined with a pronoun: I live in London, which is in England. Theere, I live in London is the first clause, and which is in England is the second clause. The word which is a pronoun that takes the place of London and joins the two clauses.

A sentence can contain many clauses, but sentences with fewer clauses are easier to understand.

 Dependent and independent clauses 
A simple sentence may also be called an independent clause. It may be a part of a compound or complex sentence, but it can also stand on its own as a simple sentence (or independent clause). 
A subordinate clause, also called a dependent clause, is one that cannot stand by itself because it does not express a complete thought. It contains both a subject and a verb. A subordinate clause always depends on a main clause.

The main clause is almost always an independent clause and so the main clause by itself makes sense and can stand on its own. However, the subordinate clause does not. For example, I love you makes perfect sense left on its own. However, and always will does not. A sentence can be made up of only dependent clauses only if it is joined by a correlative conjunction, a conjunction pair like "either/or", "neither/nor", and "not only/but also".

 References 

 Other websites 
 Clauses: the Essential Building-Blocks 
 Purdue Owl: Identifying Independent and Dependent Clauses

Category:Grammar