Molyneux's Problem

Molyneux’s question, also known as Molyneux’s problem, concerns the possibility that a person born blind might immediately identify a shape previously familiar to them only by touch if they were made to see. Through personal correspondence, William Molyneux initially presented this query to John Locke in 1688. Locke then interposed the question within the Second edition of his An Essay Concerning Human Understanding:

“Suppose a Man born blind, and now adult, and taught by his touch to distinguish between a Cube, and a Sphere of the same metal, and nighly of the same bigness, so as to tell, when he felt one and t’other, which is the Cube, which the Sphere. Suppose then the Cube and Sphere placed on a Table, and the Blind Man to be made to see. Quære, Whether by his sight, before he touched them, he could now distinguish, and tell, which is the Globe, which the Cube"
—Locke, 1694

Molyneux’s question soon became a fulcrum for early research in the epistemology of concepts, challenging common nativist intuitions about concept acquisition; asking whether sensory features distinguish concepts and how concepts may be applied in novel experiences. The question was reprinted and discussed by a wide range of early modern philosophers, including Gottfried Leibniz, George Berkeley, and Adam Smith, and was perhaps the most important problem in the burgeoning discipline of psychology of the 18th century.