Post-behavioralism emerged in the late 1960s as a significant intellectual movement within political science, primarily as a critique of the perceived shortcomings of behavioralism. While behavioralism emphasized empirical rigor, quantification, and value-neutrality, its critics argued that it often led to an obsession with methodological precision at the expense of addressing pressing social and political problems. The 'Credo of Relevance' became the rallying cry of post-behavioralism, advocating for a political science that is not only empirically sound but also socially engaged and practically useful.

The 'Credo of Relevance' essentially means that political inquiry should be directly applicable to real-world issues and contribute to their resolution. It calls for political scientists to move beyond mere description and explanation to actively engage with policy-making and social change. This emphasis on practical application and problem-solving naturally leads to the advocacy for 'action science.'

Action science, in this context, refers to a research approach that combines scientific inquiry with practical intervention and social action. It is not merely about studying a phenomenon but about actively participating in efforts to change or improve it. For post-behavioralists, action science embodies the spirit of relevance by:

1. Bridging the gap between theory and practice: It seeks to ensure that theoretical insights are translated into actionable strategies for addressing societal challenges, such as poverty, inequality, conflict, or environmental degradation.
2. Promoting social responsibility: It encourages political scientists to use their expertise to contribute to the public good and to advocate for policies that promote justice and human welfare.
3. Emphasizing problem-solving: Instead of focusing solely on abstract models or statistical correlations, action science prioritizes identifying and solving concrete problems faced by communities and societies.
4. Engaging with stakeholders: It often involves collaborative research with practitioners, policymakers, and affected communities, ensuring that research questions are relevant and that findings are directly applicable.

In essence, the 'Credo of Relevance' in post-behavioralism transformed the role of political science from a purely academic discipline to one with a strong commitment to social utility. By advocating for action science, post-behavioralists sought to make political inquiry a dynamic force for positive change, ensuring that knowledge generated by the discipline was not just accurate but also meaningful and impactful in the real world.