Book excerpt: Contemporary society very often asks of individuals and/or corporate entities that they perform actions connected in some way with the immoral actions of other individuals or entities. Typically, in the attempt to determine what would be unacceptable cooperation with such immoral actions, Christian scholars and authorities refer to the distinction, which appears in the writings of Alphonsus Liguori, between material and formal cooperation, the latter being connected in some way with the cooperator's intention in so acting. While expressing agreement with most of Alphonsus's determinations in these regards, Cooperation with Evil also argues that the philosophical background to these determinations often lacks coherence, especially when compared to related passages in the writings of Thomas Aquinas. Having compared the philosophical approaches of these two great moralists, Cooperation with Evil then describes a number of ideas in Thomas's writings that might serve as more effective tools for the analysis of cases of possible immoral cooperation. The book also includes, as appendixes, translations of relevant passages in both Alphonsus and Thomas.