The Introduction gives an overview of the book’s most important findings and contributions. Since international relations are anarchical and international legal norms are incomplete or in tension with other norms, there is potential for contestation whenever a general norm is applied to specific situations. The reactions of others to proposed norm interpretations can alter norms and their strength. The second section describes the book’s rhetorical approach, and the third section summarizes the main theoretical contributions. First, the "alternate endings" typology shows that it matters whether dispute parties (dis)agree on the norm frame or behavioral claim. Frame agreement is an internal source of stability. Moreover, the typology can guide assessment of how contestation affects norm strength. Second, I describe the focus on audience reactions, argumentation, and speakers (including delegation to agents) when analyzing extrinsic influences on the persistence of norm interpretations, and thus of alternate endings. The fourth section discusses the main contributions to the existing literature on norm strength, the dual quality of norms, legal argumentation and interpretive communities, and delegation to courts and other relevant agents. The Introduction then discusses the research design and methodology, before concluding with an overview of the remaining chapters.

This chapter focuses on the "alternate endings" typology. Building on theories of political rhetoric, we can break norms down into norm frames (norm-based justifications) and behavioral claims (conclusions for actions) and identify four alternate endings of norm contestation: norm impasse, norm neglect, norm recognition and norm clarification. Whether states (dis)agree on frames, claims, or both affects the stability of these alternate endings and norm strength. As identifying frames and claims in actors’ interpretations of international law is the cornerstone of this book, this chapter first provides detailed guidance on different kinds of norm frame and claim disagreements. It then analyzes the relative stability of each "alternate ending" and shows that frame agreement is an internal source of stability. Norm strength is conceptualized as the extent of collective expectations related to applying a norm of international law in a certain way. Norms are stronger when these collective expectations are clearer (social norm strength), and are held by more (critical) actors and/or cover more situations (relative norm strength). The chapter shows that the "alternate endings" typology can anchor the assessment of how contestation affects collective expectations. This approach provides a more actor-centric assessment of norm strength, compared to other prominent approaches.

Dominant approaches to norm development have shaped and limited the direction and impact of the norm research programme. While early work tended to characterise norm development in relatively teleological and progressive terms, more recent work has explored how a norm’s meaning changes through processes of interpretation, contestation, and violation. In spite of this important corrective and the rich debates that have emerged from it, understandings of norm development have continued to be hampered by a focus on behavioral measures and on changes in norm content. As a result, approaches to norm development remain incomplete, most notably in their neglect of norm strength. To address these shortcomings, this chapter critically reviews existing scholarship on norm change and development, highlighting the need to consider norm content and norm strength as distinct and constitutive elements in processes of norm development. The chapter proposes a typology that identifies four forms of norm change, along with an updated conceptual framework for understanding norm development. This conceptual framework overcomes existing conceptual gaps and inconsistencies in the study of norm processes. In so doing, it promises to advance existing theoretical debates, open new directions of inquiry, and contribute to the further accumulation of knowledge about international norms.