The first section of this chapter shows that, several exceptions notwithstanding, Morgenthau’s human-nature realism is unscientific, deterministic, and unduly pessimistic. The second section focuses on his inconsistent formulations of realist “political morality.” The third section argues that Morgenthau presents realism’s “signpost” (national interest defined as power) in a contradictory manner as a guide to both a descriptive theory and a prescriptive theory. This problem is compounded by the ambiguity of the concepts of national interest and power in his writings. The fourth section highlights the contradiction between Morgenthau’s declaration of their survival as an inescapable aim of all states and his on-and-off support for the creation of a world state. As the fifth section shows, Morgenthau’s comments on “the balance of power” entail three overlapping sets of contradictory positions, which depict inter-state power balancing as: (1) an inescapable reality and an unreality; (2) a natural outgrowth of the struggle for power and a desirable goal that requires skilled diplomacy; (3) a rational prescription for foreign policy and as something the rational state must avoid by pursuing hegemonic power. These problems explain why Morgenthau’s unclear realism mainly served as “both a goad and a foil” in the evolution of realism. They also explain why radically different theories could be associated with realism.