When people worry about 'witchcraft' in Soweto, they almost always have in mind the possibility that malicious persons are using harmful substances known generically, in the Zulu lingua franca of these parts, as muthi. When traditional healers administer aid to patients in distress, they almost always dispense substances also known generically as muthi. The term muthi (spelled muti in Xhosa transliterations) derives from the Nguni root -thi, signifying 'tree.' Usually translated into English as either 'medicine' or 'poison,' with the anodyne 'herbs' used in ambiguous instances, muthi refers to substances fabricated by an expert hand, substances designed by persons possessing secret knowledge to achieve either positive ends of healing, cleansing, strengthening, and protecting persons from evil forces, or negative ends of witchcraft, bringing illness, misfortune, and death to others or illicit wealth and power to the witch. . . . To understand the sorts of things people worry about when they worry about exposure to invisible evil forces in places like Soweto, it is essential to understand the various ways in which people interpret the agency inherent in substances categorized as muthi and the ways in which both human persons and invisible beings interact with them. The distinction between healing and its antithesis, witchcraft, is an essentially moral one, based on interpretations of the motives of persons deploying muthi and the ends to which these forces are directed. Witches seeking to cause harm work with muthi as poison; healers seeking well-being work with muthi as medicine. Though directed toward health and well-being—a general condition of bodily health, spiritual ease, and social harmony referred to as impilo (in Zulu; phela, Sotho)—the muthi of healers also brings death. When a healer sets out to cure a person afflicted by witchcraft, he or she will typically promise that their muthi will return the evil forces by the witch to their source, thereby killing the witch. Such violence, however, is legitimate, for it is executed in the name of defense. Witches, by definition, are engaged in illegitimate uses of the powers of muthi. In everyday discourse when Sowetans refer to witchcraft, they do not usually trouble themselves with distinctions between people enjoying innate capacities to direct evil forces, people with secret knowledge about the evil uses of muthi, and people purchasing muthi from professionals for their own nefarious purposes. Each and every person deploying muthi for malicious or illegitimate ends—such as, say, accumulating excessive wealth or power—is spoken of as a 'witch.'
Adam Ashforth, Witchcraft, Violence, and Democracy in South Africa (Chicago, IL: University of Chicago Press, 2005), 133, 133–34.