An anthropologist, Mary Douglas, some years ago wrote a book under the same title as this column. It was really about the dangers associated in early people's minds with impurity. One aspect of this is the proclivity to dietary restrictions in several early religions: An invocation by the Jewish prophet Jeremiah makes the point:" I have made you an assayer of my people-a refiner. You are to note and assay their ways. They are bronze and iron, they are all stubbornly defiant; they deal basely, all of them act corruptly." The unspoken implication is that only incorruptible gold is virtuous. A jeremiad indeed!Modern materials science, however, is full of instances of beneficial impurities… only then they are not called impurities, but dopants or additives. Names alter with circumstances: I am resolute; you are obstinate; he is stubborn.
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