1. A complex sentence is a sentence composed of at least one main clause and one subordinate clause (that cannot stand alone as a complete sentence). A complex sentence is often used to make clear which ideas are most important, and which ideas are dependent.
Model:
The people slipped into dejection under the seemingly endless rain that pelted down day after day.
a) The people slipped into dejection under the seemingly endless rain (main idea); b) that pelted down day after day (subordinate idea).
2. The subordinate clauses function grammatically as subject, object, predicative, attribute or adverbial modifier in a main clause. Accordingly, there are five types of subordinate clauses: the subject clause, the predicative clause, the attributive clause, the object clause, and several types of adverbial clauses.
Models:
It is obligatory that we finish this assignment before class ends (the subject clause).
A law of physics is that energy in any system cannot be created or destroyed (the predicative clause).
Artificial intelligence is concerned with designing computer systems that perform such tasks as learning new skills (the attributive clause).
Robert Merton studied how society influences the development of science (the object clause).
Because the world is getting warmer, polar bears are in danger of becoming extinct (the adverbial clause).
3. Complex sentences can contain two or more subordinate clauses, besides the principal clause:
Model:
I knew a man, who believed that, if a man were permitted to make the ballads, he shouldn’t care who made the laws of the nation.
a) I knew a man (the principal clause); b) who believed (the attributive clause); c) if a man were admitted to make the ballads (the adverbial clause); d) that he shouldn’t care (the object clause); e) who made the laws of the nation (the object clause).
A subordinate clause may follow, precede or interrupt the principal clause:
Models:
Each bowler rolls the ball twice in each frame,