Molyneux's Question

The celebrated Molyneux's question was addressed by the polymath Dublin lawyer, politician, and mathematician William Molyneux to John Locke, and is mentioned by Locke in Book II, Chapter IX of AnEssayConcerningHumanUnderstanding(1690). The question was as follows:

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…. Suppose then the cube and sphere placed on a table, and the blind man be made to see: query, whether by his sight, before he touched them he could now distinguish and tell which is the globe, which the cube … ? (Hoffman, p. 18)

In considering the question in the light of subsequent research, it is important to be clear that the question is not about the relative role of genes and environment in shaping visual perception. Both Molyneux and Locke assumed that the blind man would have perfectly clear and normal visual perceptions once the optical impediment to vision was removed. Otherwise, the question would be trivial. If the cured blind man could not see the object before him, obviously he would not be able to name it. Locke assumed that what he called the “annexation” of nonarbitrary “primary qualities” and arbitrary “secondary qualities” to optical input was innate. It did not occur to him that we might have to “learn to see” in the modern sense.

The actual question is about what we should now call visuo-tactile transfer. Molyneux argued that the newly recovered blind man would clearly see the object before him, but would not be able to name it, because he had names only for objects experienced through touch.

The question became a cause célèbre at the close of the 17th century and for much of the 18th, and was debated by philosophers (e.g., Berkeley, Votaire, Condillac, Diderot, and Reid). To see why it involved such a point of principle, it is helpful to jump to George Berkeley's “New Theory of Vision” (1709), where the battleground between the new philosophy and innate ideas is clearly defined. Berkeley begins by asking what would be required of the mind of the person who could recognize by sight an object that he or she had previously only felt. Logically, there would have to be some connection between the representation, or idea (as Berkeley and other empiricist philosophers termed it), of the object in the visual system and in the tactile-haptic system. Basic to the emerging empiricist philosophy was the proposition that sensory impression gave rise to ideas, and that these ideas were the only way in which we could obtain true knowledge of the outside world.

The next stage in the argument is the proposition that there is no resemblance between the ideas derived from different senses, in particular none between the visual idea of an object and its tactile-haptic counterpart. Therefore, we can establish a connection between the two ideas only by experience. Repeated temporal associations between a visual idea and a tactile-haptic idea will cause them to become connected through an “association of ideas,” as David Hume was later to suggest in A Treatise on Human Nature. The alternative [Page 567]was that the two sensory ideas could be connected through some third idea: a “general idea,” transcending the senses. If a general idea transcends the senses, it cannot be derived from experience, and must be innate. Thus, the answer to Molyneux's question must be no, or one would have to concede that there are innate, suprasensory general ideas, such as the “general idea of a triangle,” an example which Berkeley caustically derides.

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