This work argues that in order to understand and determine the morality (or immorality) of a human action, it must be considered in relation to the system of human practices within which it is performed. It argues that such an approach is to be found in the natural law theory of Thomas Aquinas, especially once it is recognized that the logical structure of Aquinas' ethical theory is basically that of an Aristotelian science. 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 relationship between will and intellect, and the principle of double effect.
