What do Policies Implicitly Assume -and what Happens when Those Assumptions Don't Hold?

Introduction Health policies frequently assume conditions that do not hold in real-world health systems, shaping outcomes in ways that are rarely examined. While policies are often evaluated on the basis of design quality, coherence, and stated objectives, less attention is paid to the implicit assumptions embedded within them and how these assumptions influence policy effects once policies enter complex and uneven system contexts. Methods This paper adopts a conceptual analytical approach, drawing on contemporary health policy and health systems literature. Rather than evaluating a specific programme or presenting new empirical data, the analysis synthesises existing scholarship to identify and examine common assumptions that underpin health policy design and assessment. Results The analysis identifies several recurring assumptions implicit in health policies, including expectations of stable system capacity, reliable administrative functioning, predictable user behaviour, and seamless coordination across service levels. When these assumptions do not hold, responsibility for making policies work is often shifted onto institutions and individuals, shaping access, experience, and outcomes in uneven ways. These dynamics help explain why policies that appear sound on paper may produce variable effects in practice. Discussion and Conclusion Unexamined policy assumptions play a critical role in mediating the relationship between policy intent and real-world outcomes. By making these assumptions explicit, this paper reframes policy effectiveness as dependent not only on policy design but also on the realism of underlying expectations. Recognising and interrogating what policies implicitly assume is essential for developing health policies that are responsive to system constraints and population realities.