ABSTRACT Metaphors are crucial in politics, conveying complex information in simple terms. Research in political science often focuses on how elites strategically use metaphors to frame issues and how citizens rely on them to reason about unfamiliar topics. However, what happens when legislators face novel problems they must attend promptly yet lack profound knowledge about? How do they reason about such issues? Building on research concerning how scientists employ metaphors (constitutive metaphors) to develop scientific theories, this paper contends that legislators can turn to metaphors when grappling with unfamiliar legislative issues. Constitutive metaphors give legislators the terminology needed to adapt their understanding of such issues. By creating a ‘theory’ of the problem, constitutive metaphors influence where legislators believe intervention is needed, ultimately shaping their policy decisions. However, metaphors inherently oversimplify, emphasizing certain aspects while ignoring others. The paper illustrates this argument using the first congressional debates in the U.S. on domestic violence legislation (1977–1978). It demonstrates how the epidemic metaphor emerged and guided policymakers, transforming their approach from victim-focused initiatives to a criminal justice perspective. Revealing the impact of constitutive metaphors on legislative reasoning offers valuable insights into unexpected dynamics within the policymaking process, including unexpected transformations in issue framing.