Although most natural law ethical theories recognize moral absolutes, there is not much agreement even among natural law theorists about how to identify them. The author argues that in order to understand and determine the morality (or immorality) of a human action, it must be considered in relation to the organized system of human practices within which it is performed. In order to depict this structure and to explain how it bears upon the analysis of action, the author investigates a number of issues that have attracted the attention of Thomistic and Aristotelian scholarship. He examines the nature of practical reason, its relationship with theoretical reason, the derivation of lower from higher ethical principles, the incommensurability of human goods, the relationship between will and intellect, and the principle of double effect.