Abstract
The study deals with the main aspects of substance in the works of Aristotle. The presence of a plurality of values for substance is the central idea of the study; in particular, substance has 1) the value of living biological entity and 2) the value of form of the biological entity; both values are fundamental components of Aristotle's theory of substance. The prevalence, in the works of Aristotle, of the first or of the second of the two values depends on the prevailing research interest of Aristotle in each work. The idea of a continuity in Aristotle's interpretation of substance in Aristotle's works is endorsed. This research treats, moreover, of the role of form as actuality, of the relations between form and matter in the material entities, and of the problem of the unity of definition.