Don't you see the natural progression? You can see it going backwards but not going forwards: Marriage is a union between a man and a woman of the same race and class arranged by their parents. Marriage is a union between a man and a woman of the same race and class. Marriage is a union between a man and a woman of the same race. Marriage is a union between a man and a woman. - WE ARE HERE - Marriage is a union between two people. Marriage is a union between people. Marriage is a union. (I'm implying that at this state animals are involved, but I want to keep the same form of decreasing the definition and therefore the meaning of marriage.) Marriage is meaningless. It isn't a slippery slope because the pattern of progression has already been demonstrated.