The English School of international relations theory (sometimes also referred to as liberal realism, the International Society school or the British institutionalists) maintains that there is a 'society of states' at the international level, despite the condition of anarchy (that is, the lack of a global ruler or world state). The English school stands for the conviction that ideas, rather than simply material capabilities, shape the conduct of international politics, and therefore deserve analysis and critique. In this sense it is similar to constructivism, though the English School has its roots more in world history, international law and political theory, and is more open to normative approaches than is generally the case with constructivism. English School scholars distinguish between international system and international society. The former is a quasi-physical realm, as proximate actors interact with one another. The latter is an intersubjective realm where actors are bound together through rules, norms and institutions. The classical English school starts with the realist assumption of an international system that forms as soon as two or more states have a sufficient amount of interaction. It underlines the English school tradition of realism and Machtpolitik (power politics) and puts international anarchy at the center of International Relations Theory. Hedley Bull defined the international system as being formed "when two or more have sufficient contact between them, and has sufficient impact on one another's decisions to cause them to behave as part of a whole." Hedley Bull, however, argued that states share a certain common interest (usually the "fear of unrestricted violence") that lead to the development of a certain set of "rules". He thus defined an international society as existent when: ...a group of states (or, more generally, a group of independent political communities) which not merely form a system, in the sense that the behaviour of each is a necessary factor in the calculations of the others, but also have established by dialogue and consent common rules and institutions for the conduct of their relations, and recognise their common interest in maintaining these arrangements.