1. logical - illogical: Her speech was so illogical2. responsible - irresponsible: I've never thought he's such an irresponsible person3. believable - unbelievable: The pain was inbelievable 4. possible - impossible: It's impossible to sleep when you are surrounded by noise5. active - inactive: Being inactive is not so good for your health6. balanced - unbalanced: He became unbalanced after his dog died7. forgettable - unforgettable: My wedding was an unforgettable occasion