In 1688 William Molyneux posed a question to John Locke: Suppose a man was born blind and knew objects like globes and cubes by touch alone, if he were suddenly to receive his sight, would he be able to point to the globe and the cube and call them by name when seeing them for the first time? Both Locke and Molyneux thought the newly sighted man would fail.

Locke, however, wrote little in explaining his response to Molyneux’s question or grounding it in his theory of ideas. My aim is to provide a comprehensive explanation for Locke’s negative answer by focusing closely on the textual and drawing on other key aspects of his philosophy. I believe Locke is interested in Molyneux’s newly sighted man as a heuristic to help us distinguish the ideas we receive from passive sensation from the complex ideas that arise from active processes of the mind. The newly sighted man is someone who has the same sensory experiences as ordinary, experienced perceivers, but who lacks the experience needed to make customs of association in the mind. These customs of association are necessary for us to “see” in three-dimensions, according to Locke, and having visual ideas of globes and cubes is necessary for connecting visual globes with tactile ones.

Locke’s negative answer to Molyneux’s question is generally considered to be problematic in light of his views on common sensibles (ideas of diverse senses) and his resemblance thesis (ideas of primary qualities resemble primary qualities in objects). I argue that my interpretation of Locke’s response to Molyneux’s question is consistent with his views on common sensibles and the resemblance thesis, once they are correctly understood.