Chapter 14 dealt with how a basic clause pattern can be expanded with words, phrases and non-finite clauses, so that the clause remains a single finite clause or a simple sentence. But a simple sentence can be expanded with a finite clause as well in two ways – (1) another finite clause (already expanded or otherwise) can be added to it, or (2) another finite clause can be embedded into it. In the first case, the result is a compound sentence and the attached clause is called a coordinate clause. More than one co-ordinate clause can be added in this way. If a finite clause is embedded within a finite clause, this embedded clause is called a subordinate clause and the result is a complex sentence. The host clause in a complex sentence is called the main clause or the matrix clause. More than one clause can be embedded in this way. The sentence resulting from both these processes is called a compound complex or mixed sentence. Since the resulting sentence is a single sentence, the process of adding a co-ordinate clause or embedding a subordinate clause is also accompanied by some other processes or changes dealt with in this chapter. But since the adding of a co-ordinate clause is a slightly simpler process, we take it up first.