What happens when Ammonium is formed, when this guy combines with this guy? Well, we get ammonia and Ammonium will not want to exist in this state because it's a relatively strong conjugate acid. So it will want to dissociate back into our ammonia. But now it dissociates back into ammonia in the presence of water. And when water is in the mixture, what happens? Well, this guy is an acid, so this guy must be a base.