Purpose Purpose clause usually comes after the main clause. I have a safe for valuables at home for the fear that a thief break in. Purpose clauses are introduced by these conjunctions: for fear that (formal), lest (formal), in order to, in order not to, in order that, so as to, so as not to, so that. Reason Reason clauses can be before or after the main clause. As it's a cloudy day, I'll take an umbrella. I'm studying hard because I want to pass my exams. Reason clauses are introduced by these conjunctions: As, because, in case, since.