A unique thesis of Tiantai Buddhism is the claim that human nature contains evil and that even the Buddha cannot be completely rid of his evil nature. The thesis was most vigorously defended and developed by a Tiantai monk, Zhili (ad 960–1028). This thesis has attracted a lot of discussion among Tiantai scholars. Their debate focuses on whether this thesis is truly representative of the original doctrine of the Tiantai founder, Zhiyi (of the sixth century ad). In 2000, Brook Ziporyn published a book Evil and/or/as the Good, which offers Tiantai's evil-nature thesis a novel explanation and justification. This book sparked a series of discussion on whether evil is not only necessary but also ‘valuable’. This present project gives an overview of these debates and provides a fresh insight on the topic.