Pollution ideas work in the life of society at two levels, one largely instrumental, one expressive. At the first level, the more obvious one, we find people trying to influence one another’s behavior. Beliefs reinforce social pressures: all the powers of the universe are called in to guarantee an old man’s dying wish, a mother’s dignity, the rights of the weak and innocent. Political power is usually held precariously and primitive rulers are no exception. So we find their legitimate pretensions backed by beliefs in extraordinary powers emanating from their persons, from the insignia of their office or from the words they can utter. Similarly the ideal order of society is guarded by dangers which threaten transgressors. These danger-beliefs are as much threats which one man uses to coerce another as dangerous which he himself fears to incur by his own lapses from righteousness. They are a strong language of mutual exhortation. At this level the laws of nature are dragged in to sanction the moral code: this kind of disease is caused by adultery, that by incest; this meteorological disaster is the effect of political disloyalty, that the effect of impiety. The whole universe is harnessed to men’s attempts to force one another into good citizenship. Thus we find that certain moral values are upheld and certain social roles defined by beliefs and dangerous contagion, as when the glance or touch of an adulterer is held to bring illness to his neighbors or his children.
From Mary Douglas’s study of pollution and taboo, Purity and Danger.