Albus sighed, again. "You know I can't do that," he said, rehearsing an old argument. He usually pointed out that Potions professors were harder to replace than Defense professors, and in ten years he'd never found anyone who could take the job he'd given Severus. The Head of Slytherin House would make a fine Defense Against the Dark Arts professor, Albus suspected, if not a happy one. Severus knew he would do it better than some of the failures they'd had of late, which was why they kept having this argument. But even if Albus could find a new Potions Master - "I need you for longer than a year, Severus."