The following two sentences show how you should focus on the clause and not the entire sentence to choose the right pronoun. A run on sentence occurs when two or more independent clauses (also called complete sentences) are not properly related to each other. All sentences must have at least one independent clause. A subsidiary sentence has a subject and a verb, but cannot be alone, unlike an independent sentence. It depends on something else in the sentence to express a complete idea, which is why it is also called dependent clause. Some subsidiary sentences are introduced by relative pronouns (who, who, what, what, who) and others by subordinate conjunctions (although, if, except when, etc.). Subsidiary sentences act as adjectives, nouns and adverbians.