jats:pA philosophical debate between particle physicists and solid state physicists roiled as these subdisciplines competed for financial support, social approbation, and intellectual prestige through the second half of the twentieth century. Their disagreement hinged on the nature of fundamental research. The particle physics community adopted a reductionist approach, arguing that the fundamental physical laws were those governing the smallest constituents of matter and energy. Partly in response to this position, solid state physicists developed a range of more permissive perspectives on what type of physics could be fundamental, all of which stressed the importance of higher-level characteristics, maintaining that investigations at many levels of complexity might yield fundamental insight. This paper traces the dispute over fundamentality, which grew both from the specific problems physicists encountered while building their professional infrastructure, and from the demands of funding their research in Cold War America. Through an exploration of how physicists developed philosophical positions within institutional contexts and deployed those positions in their rhetoric, I argue first that professional pressures both motivated and exerted influence over the construction of such views, second that philosophical views had a reciprocal guiding effect on the institutional and professional development of Cold War physics, and third that these views were further bent, blunted, and reshaped when deployed in high-stakes rhetorical discourse. The case studies through which this story unfolds indicate that further attention to such philosophical commitments is warranted when examining the historical development of scientific institutions, communities, and hierarchies.</jats:p>