Error is a neglected epistemological category in the history of science. This neglect has been driven by the commonsense idea that its elimination is a general good, which often renders it invisible or at least not worth noticing. At the end of the sixteenth century across Europe, medicine increasingly focused on “popular errors,” a genre where learned doctors addressed potential patients to disperse false belief about treatments. By the mid-seventeenth century, investigations into popular error informed the working methodology of natural (...) philosophers, rather than just physicians. In 1646, Thomas Browne published Pseudodoxia Epidemica, a large volume on popular error. Despite Browne’s formal training as a physician, this work examined only a few medical errors and instead aspired to be an encyclopedia of error. Pseudodoxia Epidemica was highly popular, running to six editions, and was known by the Fellows of the Royal Society. Influenced by Browne, alongside Bacon’s theory of the idols, natural philosophic practice in the late sixteenth and seventeenth century developed a focus on error that revised traditional attention to the discovery of knowledge. Fellows such as Robert Boyle and Robert Hooke proposed new ways to secure truth under the far-reaching influence of Bacon’s refutations of “natural human reason” distorted by false idols, of syllogistic logic, and of “theories,” his label for traditional philosophical systems that bias thought toward falsity. In three parts, this article traces the progression in early modern scientific approaches to handling error, and especially medical error – from physicians’ efforts to identify and eradicate it through collaborative effort, to the striking tension in Browne’s work between seeking to eliminate error while also showing a marked tolerance for it, to the Royal Society’s Baconian objective of instrumentalizing error to find truth. Error emerges as its own epistemic category that serves as a driving force toward knowledge production. (shrink)