What can we learn from the detailed exegesis of Carl von Clausewitz for the study of strategy? Based on a detailed reading of Clausewitz' book On War, this paper proposes that Clausewitz' reflections on strategy unfold along two parallel arguments. First, he explores the principal difficulties of a positive theory of strategy. This critical inquiry shows how quantities and qualities influence each other in war; how events emerge rather uncontrollably from the interplay of action and reaction; and how the fog of war puts a veil of uncertainty over all information. Clausewitz's fundamental critique leads him to the conclusion that a normative theory of strategy is impossible. Clausewitz' second stream of thought investigates how strategy could be studied instead. On the one hand - and based on his famous dictum that war is the continuation of politics by other means - he suggests understanding strategy as a socio-political (rhetorical) mechanism through which people can be convinced in deliberations about a specific course of action. On the other hand, Clausewitz also reflects on the pedagogy of strategy. He concludes that theory may be useful to educate the mind of the future leader, but not to accompany him on the battlefield. The contribution this paper hopes to make to The Age of Strategy: Exploring the Cultural, Organizational, and Political Dimensions of Strategy is twofold: first, the study of Clausewitz represents a contribution to the study of the history of strategic thought. The second contribution is aimed at the relation between strategy as theory and practice. Following Raymond Aron's suggestion, On War does not offer a normative doctrine but rather a critical theory that equips the student of strategy to understand the task at hand 'without entertaining any absurd claim to communicate the secret of victory.'.