by Charlie Huenemann
How much of the world do we actually experience? Of course, I'm not bemoaning the shortness of human life, or the narrow range of the visual spectrum, or the insensitivities of our skins and tongues. There's no doubt we're missing out on a lot. But within the world of our experience – how much of it do we in fact experience?
This is a big question always, but it was particularly big over the course of the 17th and 18th centuries. Some thinkers abided by the scholastic dictum – “there's nothing in the mind that isn't first presented by the senses” – which means that all of the content in our model of the world is gained through sensory experience. There is something very neat and tidy about this – nothing comes from nothing, and everything is accounted for.
Other philosophers found, as they carefully parsed their own sensory experience, that there was a lot less in it than they thought. We see patches of colors, not objects; we see sudden bright changes, and hear loud booms, and it is only with some mental effort that we combine them into a single event; we observe one change, and another, and we only come to think of the changes as causally related. The senses surely give us some data, these philosophers believed, but the mind is required to structure these data into a world. There is order in our experience that does not come from the senses.
The general debate became focused on a thought experiment raised by William Molyneux in a letter to John Locke (1693):
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.
Those of us used to coordinating sight and touch must make some effort to imagine what it would be like to see a sphere and a cube for the first time, without already knowing from experience what each would feel like, were we to reach out and touch it. Without having had that experience, would it be obvious that one shape would feel sphere-y, and obvious that the other would feel cube-y?
Molyneux's problem, by the way, was rooted in his own experience. In 1678 he had married Lucy Domville – “a lady noted for intelligence, amiability, and great beauty.” But just a few months into the marriage, Lucy fell ill and became blind. The diagnosis is unclear. She lived in constant pain for another thirteen years, dying just two years before Molyneaux was to send his letter to Locke. It is said that Molyneux had turned to mathematics and philosophy over this dark period as a means for coping with his frustration at not being able to do anything to help his wife. Those heady distractions led eventually to his own fame, as he founded not only the Dublin Philosophical Society but also helped to found or inspire several other organizations that promoted sharing scientific discovery. He went on to argue for equal rights for Ireland, only to see his book burned during the reign of William and Mary. He died in 1698 of kidney disease.
Back to the main story. John Locke was firmly within the neat and tidy “nothing in the mind that doesn't come from the senses” party, so he ruled that the Man would not be able to tell sphere from cube by sight alone. Leibniz was on the other side of the debate. In his commentary and critique of Locke, he prepared his answer with utmost care:
[Let us assume] a condition which can be taken to be implicit in the question: namely that it is merely a problem of telling which is which, and that the blind man knows that the two shaped bodies which he has to discern are before him and thus that each of the appearances which he sees is either that of a cube or that of a sphere. Given this condition, it seems to me past question that the blind man whose sight is restored could discern them by applying rational principles to the sensory knowledge which he has already acquired by touch [….] My view rests on the fact that in the case of the sphere, there are no distinguished points on the surface of the sphere taken in itself, since everything there is uniform and without angles, whereas in the case of the cube there are eight points which are distinguished from all the others.
What the Man could observe, according to Leibniz, is that one of these shapes has a homogeneous surface, and the other does not; and since he knows from his previous experience of touch that a sphere feels homogeneous and the cube does not, he should be able to figure out which was which, from his new sight alone.
For Leibniz, the mind informs our experience with rational principles. In this case, the rational principle at work is that differences found in one sensory domain must transfer to the others. (Actually, that statement is too strong. Some differences might not transfer: think of Bertie Bott's Every Flavour Beans, whose flavors vary in dramatic ways even when they look identical. This is why Leibniz insisted on the condition that the Man know in advance the nature of the choice being presented to him.)
The world didn't have to wait long for an actual Molyneux case, though it came too late for Molyneux, Locke or Leibniz (let alone poor Lucy). In 1728, the English physician William Cheselden restored sight to a 13-year-old boy who had been blind since birth. (One imagines a convoy of carriages loaded with philosophers racing to the scene, each armed with cubes and spheres.) Well? The result? Hard to say. As Cheselden reported:
When he first saw, he was so far from making any judgment of distances, that he thought all object whatever touched his eyes (as he expressed it) as what he felt did his skin, and thought no object so agreeable as those which were smooth and regular, though he could form no judgment of their shape, or guess what it was in any object that was pleasing to him: he knew not the shape of anything, nor any one thing from another, however different in shape or magnitude; but upon being told what things were, whose form he knew before from feeling, he would carefully observe, that he might know them again.
But it sounds like a win for Locke.
Still, recent experiments suggest that while it takes some experience to begin to parse the data from newly-acquired vision, people take to the task pretty quickly. It may be that some of Leibniz's rational principles are indeed at work, but just buried deeper in the process.
Degenaar, Marjolein and Lokhorst, Gert-Jan, “Molyneux's Problem”, The Stanford Encyclopedia of Philosophy, URL = <http://plato.stanford.edu/archives/spr2014/entries/molyneux-problem/>.
Glenney, Brian, “Molyneux's Question”, The Internet Encyclopedia of Philosophy, URL = <http://www.iep.utm.edu/molyneux/>.
O'Conner, J. J. and E. F. Robertson, “William Molyneux”, URL = <http://www-history.mcs.st-and.ac.uk/Biographies/Molyneux_William.html>.