The role of intuition in scientific endeavor is examined through the lens of three philosophers/historians of science—Karl Popper, Thomas Kuhn, and Gerald Holton. All three attribute an important role to imagination/intuition in scientific endeavor. As a case study, the article examines the controversy between the generally accepted Vesicular Sequestration/Exocytosis Model of pancreatic digestive enzyme secretion and an alternative view called the Equilibrium Model. It highlights the intertwining of intuition and reason in the genesis of the Equilibrium Model developed in response (...) to findings that could not readily be explained by the consensus view. It suggests that tacit knowledge/understanding works in conjunction with philosophical and aesthetic presuppositions that function to a greater or lesser extent below awareness. Together they guide judgments about whether falsification has occurred and help frame alternative theories. (shrink)