In order to appeal to the spirit world, a diviner (sangoma) must invoke the ancestors through divination processes to determine the problem. Then, a herbalist (inyanga) prepares a mixture (muthi) to be consumed in order to influence the ancestors. As such, diviners and herbalists play an important part in the daily lives of the Zulu people. However, a distinction is made between white muthi (umuthi omhlope), which has positive effects, such as healing or the prevention or reversal of misfortune, and black muthi (umuthi omnyama), which can bring illness or death to others, or ill-gotten wealth to the user. Users of black muthi are considered witches, and shunned by society.