Also known as Afa, Ifa is the name of the Yoruba god of knowledge and of the rigidly defined and complex system of obtaining knowledge from Ifa through divination. A person consults Ifa on an occasion when he or she needs to make a significant decision, whether about a personal matter such as marriage or a political enterprise such as war. The Babalawo ("father of secrets"), a diviner and priest, consults Ifa by manipulating sixteen palm nuts, which form a large handful. He begins by holding them in both hands and then attempts to pick them all up in his right hand. If one nut remains in his left hand, he makes a double mark in wood dust on his divining tray; if two remain, he makes a single mark. Four such marks made in a vertical column constitute one half of a...