A clause is a group of word which minimum contains of verb and complement, but it may also contain of a single verb, its complement, and its adjunct. An ideal clause may contain a phrase that refers to an action, refers to people that involves to the action or state, or may refers to time and place of the action. It means that a clause minimum contains of one verb or predicate but it is not may only a verb. It may also contain a phrase or other clause that modify the verb.
Linguistics divides sentence into two central parts, they are the subject and the predicate. In the clause, predicate has a function to express an event within the clause. The term of clause refers to sentence that becomes the fundamental element of other sentence or phrase. It may coordinate with one or more than one fundamental element of sentence or clause to form a compound or complex sentence. Therefore, a simple sentence contains only one clause and a complex sentence contains at least two clauses.
A sentence is a group of words or phrases that form a statement, exclamation, or question. It has been stated above that a sentence that contains of one clause is known as simple sentence and complex sentence in the other hand contains of more than one sentence. Simple means that consisting of one sentence and complex in the other hand means that consisting of more than one clauses. Bellow is the example of the clause and sentence.
1) Those men like potato chips.
2) My friend thinks that the book which is on the table is mine.
Based on the example above, the simple sentence in (1) contains of one clause and it is known as independent sentence or clause. Simple sentence or clause is not attached to the other sentence or clause. That is why it is called by independent sentence or clause. The example (2) in other hand is called by complex sentence. It contains of more than one clause. The bold word in example above is called sub-coordinate conjunction. It is used to join together every single string of simple sentence.
The complex sentence above has one main clause and two (more than one) subordinate clauses. The term of main clause and subordinate clause indicate that the clauses do not have the same function within the sentence. The subordinate clause is contained within the main clause. In other word, it is syntactically dependent on the main clause. Therefore, the subordinate clause is a part of the main clause.
Jim Miller, Op.Cit. p 6
 Maggie Tallerman, Op.cit. p.58
 Herman Wekker and Liliane Haegman. A Modern Course in English Syntax.Taylor and Francis e-Library. 2004. P. 29
 Maggie Tallerman. Op.cit. p.77