tautology

      There are so many ways to be wrong, that to define them formally, as in a class on logic, they have each been given names.   
       A tautology is the formal name for a logical error--the error of using a thing to explain a thing. "He killed them because he's a serial killer" is a tautology. It is not an explanation, although it sounds something like one. Serial killers kill people, so that part is true. But illogical. He didn't kill them because he's a serial killer. The because renders the sentence illogical. "He killed them because he's a serial killer" makes no more sense than "it's raining because it's wet out". It may be raining out, and wet, but it isn't raining because it's wet. Wet is not the cause of the rain. Serial killing is not the cause of the murder.