 (8) Informal scientific judgment depends heavily upon rhetoric and judgments of heuristic fertility in the context of discovery—the very items that had been expressly excluded from the context of rational justification by the dominant tradition. For Kuhn, normal problem solving is a matter of modeling new puzzles solutions on established precedents, the exemplars, where modeling crucially involves judgments of similarity, analogy, or metaphor. (Whereas Popper’s methodology is a learning theory in which we learn only from our mistakes, in Kuhn’s we learn also (mainly) from our successes—the exemplars, which, over time ratchet up our knowledge within normal science.) In paradigm change, the rhetorical tropes used in persuasion are typically more abstract and tenuous than in normal science. Kuhn’s account of the rational acceptance of paradigm change had to remain thin because of incommensurability. Here the justification problem was all the more difficult because new paradigms generally lose some of the successes of their predecessors (so called “Kuhn loss” of problem solutions but also data, theory, goals, and standards).