The benign/malignant distinction for false premises

Faced with vivid cases of inferential knowledge to which false premises seem evidentially indispensable—knowledge-from-falsehood cases, or 'KFF cases'—some of us retreat from the traditional, Aristotelian view that only knowledge begets knowledge in reasoning. But KFF-ers are a minority in the debate over such cases. The epistemology of reasoning is still dominated by KDF-ers, those for whom, on close inspection, purported KFF cases turn out to be knowledge-despite-falsehood cases. Each group has its own warring factions. I belong with those who think that every KDF proposal on the market is hopeless, which saddles me with the fundamental problem for KFF-ers: the task of explaining why some false premises are knowledge-suppressing, or 'malignant', while others are knowledge-yielding, or 'benign'. Some have suggested that a satisfactory KFF view might be found within truth-tracking epistemologies, either a safety-based theory or a sensitivity-based one. I examine the hypothesis and conclude that it fails. I then turn to the defeasibility theory of knowledge, a theory that has been deployed by its chief architect, Peter Klein, in defense of a KDF stance, and argue that the desired benign/malignant distinction can be found within a properly formulated, non-Kleinian defeasibility theory.