Any sentence is a compound sentence if it consists of two clauses or more, each of which can break off into a separate independent clause that can constitute an independent sentence. Here are some examples of compound sentences and of the independent sentences they break off into:
 [compound] I went to bed and I fell asleep.
[independent] I went to bed.
I fell asleep.
 [compound] They made a profit but they still went under.
[independent] They made a profit.
They still went under.
 [compound] It began to rain when the sun was shining.
[independent] It began to rain.
The sun was still shining.
 [compound] He wanted me to arrive early.
[independent] He wanted [something].
I [should] arrive early.
These independent sentences can stand alone as separate sentences because each one constitutes a clause, so each one has its own subject and its own verb phrase.
The category compound sentences consists of two subcategories: coordinate sentences and subordinate sentences. The differences between these two subcategories are explained in detail in this chapter. For the moment it is enough to say that a coordinate sentence contains two or more clauses of equal importance that are [coordinated] with each other by a conjunction, while a subordinate sentence is divided into a main clause and a subordinate clause according to the relative importance assigned each one. In very simple terms, the main clause controls the subordinate clause and is linked to it by a conjunction.
Coordinate sentences consist of two or more clauses that are coordinated (linked together) by any one of these conjunctions: