The renewed interest in ideology and the demand by scholars like Geertz that social scientists and historians must take it seriously has prompted a crucial question: How does ideology cause foreign policy? In Geertz's work this question was intentionally evaded. In his view ideology could not be a cause of action. Ideology is a part of culture and as such acts as the context of, and provides the language and symbols for, social action. Postmodernist theorists have proven similarly uninterested in traditional questions about the causes of the phenomena they study. But for historians, the question of causes, of how things happen, is central to their project. Critics of Hunt's work have raised just this question. How, for example, did the American belief in a hierarchy of race influence particular decisions? Neither have political scientists proved willing to abandon the question of causes. Although theorists of foreign policy increasingly accept that ideas and ideology, not just interests, matter in foreign policy, for many political scientists and historians, ideology needs a "causal mechanism"—a way to act on policy—in order to be useful in explaining events.
This remains a sharply contested issue. Some scholars have focused on institutions and groups of policymakers, arguing that over time these take on a shared culture and world view that influences policy. Others have taken a biographical approach, searching through personal papers in an effort to uncover the beliefs and cultural heritage of individual policymakers. The work of the theorist Walter Carlsnaes suggests one answer to the problem of causation. Like Geertz, Carlsnaes views ideology as a contextual variable in decision making. In Ideology and Foreign Policy, Carlsnaes argues that ideology does not cause foreign policy; the decisions of statesmen do. Yet those decisions are made in a particular context, in which ideology is significant. Policymakers react to a particular situation and draw on ideological and cultural resources to make their decisions. While ideology does not intervene in international politics directly, it thus remains a significant determinant of policy by influencing the participants.
This formulation suggests an important pair of insights: Foreign policy cannot be understood in terms of ideology alone, but neither can ideology be ignored. Policymakers struggle for power and respond to threats and opportunities just as realists like Morgenthau have long held. But ideology provides a context—open to analysis in the way of Geertz—that serves to condition those responses and shape the particulars of decision making. The sociologist Max Weber, in his 1913 essay "The Social Psychology of the World's Religions," aptly envisioned ideas as determining the track along which action is pushed by the dynamic of interest. Ideas and interest are separate yet entwined. Interests come out of the context in which policymakers operate and are revealed in the language and the form of their decisions. In this way ideology, despite not serving as a direct cause of policy, remains a significant part of foreign policy.