1. Because, as, since, for, inasmuch as agree in implying a reason for an occurrence or action. Because introduces a direct reason: I was sleeping because I was tired. As and since are so casual as to imply merely circumstances attendant on the main statement: As (or since ) I was tired, I was sleeping. The reason, proof, or justification introduced by for is like an afterthought or a parenthetical statement: I was sleeping, for I was tired. The more formal inasmuch as implies concession; the main statement is true in view of the circumstances introduced by this conjunction: Inasmuch as I was tired, it seemed best to sleep.