The discoveries of the new science of the sixteenth and seventeenth centuries offered unique challenges to philosophers concerned with answering scepticism or with defending common-sense beliefs. This chapter focuses on how Descartes, Locke, and Berkeley took up those challenges. Descartes’s philosophical project brought to the forefront the tensions embedded in the confrontation between common sense, science, and scepticism. His insistence on raising the strongest sceptical doubts and on answering them with absolute certainty often left common-sense beliefs behind. Confronted with this result, and perhaps also with Descartes’s own failure to answer the sceptic, Locke weakened both the force of his own scepticism and the degree of certainty he demanded in his philosophical views. Moreover, he was often willing to privilege common-sense beliefs over arguments conflicting with them. In these ways, he provided a system which reconciled common sense, science, and scepticism more adequately than Descartes. Berkeley, convinced that his predecessors’ work left the sceptic unscathed, developed views which, he claimed, completed this reconciliation project. But the chapter shows that his views fall short of this goal. The work of these philosophers put in place the foundations upon which later thinkers would tackle this reconciliation challenge.

The Molyneux problem is a question about the nature of sensory perception that was first posed by William Molyneux, the founder of the Dublin Philosophical Society, in correspondence with the English philosopher John Locke in 1688. The problem asks whether a blind man who has learned to distinguish between different shapes by his sense of touch alone would be able, upon having his vision restored, to make the same distinctions using only his sense of sight. Molyneux’s question has been called the most important problem in the history of Irish philosophy, and the reason for its significance is the wide variety of epistemological, theological, linguistic, and aesthetic considerations to which it gave rise. This chapter identifies and documents the major stages in the early development of Molyneux’s problem in eighteenth-century Ireland, England, and France. Along the way, the chapter draws on contemporary religious analogies, surgical evidence, and fictional experiments in order to bring a new perspective to current debates about the meaning of ‘Enlightenment’ in eighteenth-century Irish intellectual culture.