Relative pronouns like <em>who</em>, <em>whom</em>, <em>which</em>, or <em>that</em> are most often used to introduce subordinate clauses, e.g. "The electric guitar <u>that my brother bought me</u> is awesome." The underlined portion is the subordinate clause, introduced by <em>that</em>, modifying the subject in the main sentence "The electric guitar." The same is true for subordinate conjunctions like <em>after</em>, <em>because</em> and <em>until</em>: "I will be waiting here <u>until you decide to return.</u>" Once again, the result is a clause (subject <em>you</em> + predicate <em>decide to</em> <em>return</em>) that, due to the subordinating conjunction, cannot stand on its own as a sentence.
