Failure to confront our own ideas about dirt has resulted in erroneous ideas about ancient purity rites. One is the idea that all such rites can be interpreted in terms of hygiene: “if we only knew all the circumstances we would find the rational basis of primitive ritual amply justified” (36). Another is the opposite view: that ancient rituals are merely symbolic and have nothing to do with modern ideas of hygiene.

Our ideas of uncleanness are founded in a knowledge of bacteria and germs that ancient societies lacked. By contrast, primitive societies’ ideas of purity were based on a classification of matter and confronting ambiguity in nature. The unclean was that which was anomalous or lay outside the given pattern. Dirt was considered to be out-of-place matter. We still hold this view more or less unconsciously today; for example, we consider muddy garden tools to be unclean only if they are indoors, or food to be potentially dirty if brought into the office. Impurity is fundamentally about order: “Before we think about ritual pollution we must go down in sack-cloth and ashes and scrupulously re-examine our own ideas about dirt” (43).