There are two types of clauses: "independent" and "non-independent"/"interdependent". An independent clause realises a speech act such as a statement, a question, a command or an offer. A non-independent clause does not realise any act. A non-independent clause (simplex or complex) is usually logically related to other non-independent clauses. Together they usually constitute a single independent clause (complex). For that reason, non-independent clauses are also called "interdependent". For instance, the non-independent clause "because I have no friends" is related to the non-independent clause "I don't go out" in "I don't go out, because I have no friends". The whole clause complex is independent because it realises a statement. What is stated is the causal nexus between having no friend and not going out. When such a statement is acted out, the fact that the speaker doesn't go out is already established, therefore it cannot be stated. What is still open and under negotiation is the reason for that fact. The causal nexus is represented by the independent clause complex and not by the two interdependent clause simplexes.