This document discusses compound sentences formed through subordination. It defines subordinate clauses and subordinators, which introduce subordinate clauses. Subordinate clauses can be nominal/noun clauses, adjectival/adjective clauses, or adverbial/adverb clauses depending on their function. Noun clauses function similar to nouns, performing roles like subject, direct object, etc. Adjective clauses modify or identify nouns, and can be restrictive/defining or non-restrictive/non-defining. Adverb clauses modify verbs, adjectives or other clauses. The document provides examples and explanations of these clause types.