Color, Space and Figure in Locke: An Interpretation of the Molyneux Problem

THIS IS HOW LOCKE, in the second edition of his Essay Concerning Human Understanding (1694), introduces a question that had been suggested to him in a letter from William Molyneux: ¹

. . . I shall here insert a Problem of that very Ingenious and Studious promoter of Knowledge, the Learned and Worthy Mr. Molineux, which he was pleased to send me in a Letter some Months since; and it is this: 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. Quaere, Whether by his Sight, before he touch'd them, he could now distinguish, and tell, which is the Globe, which the Cube. ²

In the standard interpretation of the Molyneux problem as presented in Locke, the question is always linked to the general issue of differences in the ideas of figure received by the various senses. This interpretation--put forward by Berkeley ³ --says that for Locke, the ideas of figure produced by sight are specifically different from those produced by the sense of touch. This interpretation is partially justified by the response suggested by Molyneux to his own question, a response approved of by Locke:

To which the acute and judicious Proposer answers: Not. For though he has obtain'd the experience of, how a Globe, how a Cube affects his touch; yet he has not yet attained the Experience, that what affects his touch so or so, must affect his sight so or so; Or that a protuberant angle in the Cube, that pressed his hand unequally, shall appear to his eye, as it does in the Cube. I agree with this thinking Gent. whom I am proud to call my Friend, in his answer to this his Problem . . . ⁴

The specific distinction Locke supposedly refers to is sometimes thought to relate to a difference among the number of perceivable dimensions. The idea is that in Locke, only the sense of touch can receive ideas of three-dimensional figures, whereas sight always receives two. Therefore, when we believe we see a three-dimensional space or shape, what in fact happens is that we are making a judgement that moves from a visual to a tactile idea of figure. ⁵

This "standard" interpretation is, in my opinion, inadequate. It presupposes a specific distinction between ideas of shape received by sight and those received by touch, and this distinction does not exist in Locke's philosophy. Indeed, aside from the passage in which Molyneux replies to his own question, nowhere in Locke does one find any reference to any sort of heterogeneity among visual and tactile ideas of space. Maintaining that such a distinction is a theme in Locke would depend upon an isolated case in the Essay. Rather than placing the emphasis on the differences between the two senses in the Essay, Locke stresses the mutual capacity of sight and touch to perceive the shape of bodies. Not only are ideas of figure simple ideas "we can receive and convey into our minds . . . both by seeing and feeling," ⁶ the very definition of the idea of figure considers sight and touch to be the two senses capable of perceiving the shape of a body. When one takes into account the whole of Locke's Essay, it becomes difficult to accept the existence of two heterogeneous ideas of figure, whose differences support his negative response to Molyneux's question. ⁷

One might suppose that for Locke, the Molyneux question is strictly concerned with the characteristics of processes whereby we construct general abstract ideas. His negative...