It's your belief in these things that make them work...Not the rituals themselves. If a necromancer does happen to conjure up a dead spirit (Don't flame me but all I know of necromancy is what it means and the Hollywood version of it) it's because he, or someone who has done the exact same ritual before him, believes it without a doubt in his mind. I studied magick for awhile. Mostly general stuff, but the one common thing I found is that you have to believe without a doubt in your mind something will work for it to actually work. So...Yeah. Doesn't mean you can't do necromancy though. Sounds like good dirty fun to me.