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Molyneux's Question with Janet Levin and Brian Glenney

Love & Philosophy — Beyond Dichotomy

In 1688, an Irish scientist named William Molyneux sent John Locke a letter with a question in it. Suppose a man born blind has learned by touch to tell a cube from a sphere. Suppose he is given sight, and the two objects are set on a table in front of him. Could he tell, by looking alone, which is which?

Locke said no, and put the question into the second edition of his Essay Concerning Human Understanding. Berkeley said no more emphatically. Leibniz said yes — with a hint, and a little time. And three centuries later the question is still open, only now it's being asked in operating theatres in New Delhi, in habituation studies with ten-hour-old infants, and in the way a skateboarder looks at a handrail.

Janet Levin and Brian Glenney have been in conversation about this problem since Brian's dissertation defense in 2007, where Janet was on his committee. They still disagree — productively — about whether you need to move your body in order to see. This episode is that disagreement, twenty years on.

Janet Levin is recently retired from the philosophy department at the University of Southern California. She works on the mind-body problem, phenomenal concepts, and what she calls the philosophy of philosophy: whether thought experiments are worth anything, and whether they can absorb empirical information and still count as philosophy. Her 2008 paper introduced the distinction between temporal and epistemic immediacy that has shaped how the Molyneux question is tested ever since.

Brian Glenney teaches at Norwich University in Vermont. He wrote his dissertation on Molyneux's problem at USC in 2007 under James Van Cleve and Janet Levin, wrote the Internet Encyclopedia of Philosophy entry on the question, and has since argued for a pluralist answer — that the question has many correct answers depending on who is being asked about, and how. He also works on skateboarding, urban space, and the sensory expertise he calls the skater's eye.

Full show notes

00:00 — Why a navigational approach to mind keeps running into this question
02:20 — Introductions: phenomenal concepts, sensory expertise, and Bernie Sanders at the skate park
05:20 — Janet reads Locke's own statement of the question, and his answer
08:00 — Why this was supposed to be the crucial experiment for empiricism vs. rationalism
10:30 — The 1688 letter Locke never answered, and the 1693 one he did
12:00 — Molyneux, Dioptrica Nova, and the attempt to give empiricism experimental oomph
14:00 — Why Locke buried the question in a passage about perceptual learning
15:00 — Common sensibles: what touch and sight might share
17:00 — Locke's "at first sight" trick, and what it forecloses
19:30 — Passivity vs. activity: if you move your head, is it still perception?
20:40 — Leibniz's cheat code, and the birth of epistemic immediacy
22:20 — Janet's distinction: temporal immediacy vs. epistemic immediacy
24:15 — Held (2011) and the best evidence for a "no"
27:30 — Andrea's caricature: two languages, or one idea?
29:30 — Why restored vision isn't normal vision — and the paradox that follows
31:00 — Vision and touch as English and Russian; Leibniz as the bilingual child
33:30 — Janet on phenomenal concepts and why Molyneux caught her
35:40 — Did you know Adam Smith had a theory of perception? He wrote it at fifteen
37:50 — Brian finds his own ancestor in the archive: George Glennie, Aberdeen, 1796
40:15 — The moon illusion, and how Janet and Brian actually met
41:20 — The dissertation with six chapters, and the one revision that changed everything
42:30 — Maybe there isn't a single correct answer
47:15 — Project Prakash: five subjects, three days of play, and a fast yes
51:30 — Janet's counter-proposal: what if you only tweak vision?
55:20 — Bumpy pacifiers, baby chicks, and the ten-hour-old infants who disagree
58:50 — The six-month-old who recognizes its own hand
01:01:00 — Nobody frames it as empiricism vs. rationalism anymore
01:03:20 — The couch potato perceiver and the sentient statue
01:05:50 — Could virtual reality run the experiment we can't?
01:07:00 — Path dependency: every subject arrives with a history
01:11:20 — The blind Rubik's Cube puzzler, and whether expertise transfers
01:15:00 — "Give me something I care about": motivation as the missing variable
01:19:10 — Why does perception have to be passive at all?
01:22:20 — Andrea: what if it isn't yes or no?
01:26:50 — Ned Block and the border between seeing and thinking
01:29:20 — The skater's eye: knowledge in the heel rather than the head
01:33:00 — Enactivism, affordances, and the motivation Brian adds to them
01:36:30 — Janet puts a lock on the back gate
01:39:20 — Do you still care about this? Plato's cave, Reid, and the seduction of the external world

Some words that come up

Empiricism / rationalism — The organizing quarrel of the era. Empiricists (Locke, Berkeley, Hume) hold that knowledge is built up from sense experience. Rationalists (Leibniz) hold that some ideas are innate and amodal — not owned by any single sense. Molyneux's question was supposed to settle it experimentally.

Common sensibles — Properties like shape, figure, and distance that seem accessible to more than one sense. Colour isn't one; neither is roughness. The question is whether a common sensible is genuinely shared, or whether you have to learn to correlate two separate streams.

At first sight — Locke's three-word addition, and, as Brian argues, a trick: it more or less guarantees the answer is no, if perceptual learning is needed to make the correlations.

Temporal immediacy vs. epistemic immediacy — Janet's distinction. Temporal means the first instant after the bandages come off, which is probably what Locke meant. Epistemic means the identification is made by perception rather than by inference or association — so you wait until the person actually has the wherewithal to see, and only then test. It reframes what a fair experiment even looks like.

Perceptual learning — Changes in what you can perceive that come from experience rather than reasoning. Locke's newly sighted person sees a flat, variously coloured circle before they see a sphere.

Passivity vs. activity — Locke assumed perception is passive reception, and that anything active is cognition. So: is moving your head still perceiving? Is watching an object rotate? The whole episode circles this.

The perception/cognition border — The contemporary form of the same question, now central to philosophy of mind through Ned Block's work.

Phenomenal concepts — Concepts of what it's like to have an experience: to see red, to feel something smooth. Janet's long-standing interest, and her route into Molyneux.

Affordances / enactivism — Gibson's idea that we perceive the world in terms of what it lets us do, developed by Alva Noë and others. Brian adds a motivational layer: the skater doesn't just see that the handrail is skateable, they want to skate it.

Locke, An Essay Concerning Human Understanding (1690; Molyneux's question added to the 1694 second edition), Book II, Ch. IX, §8. Full text at Project Gutenberg
Molyneux's first letter to Locke, 7 July 1688 — the one Locke never answered. The second, in 1693, is the one that made it into the Essay. Molyneux had in the meantime dedicated his optics treatise Dioptrica Nova (1692) to Locke.
Marjolein Degenaar & Gert-Jan Lokhorst, "Molyneux's Problem", Stanford Encyclopedia of Philosophy — the standard scholarly overview. plato.stanford.edu/entries/molyneux-problem
Brian Glenney, "Molyneux's Question", Internet Encyclopedia of Philosophy — Brian's own entry, and the best place to start. iep.utm.edu/molyneux
Michael J. Morgan, Molyneux's Question: Vision, Touch and the Philosophy of Perception (Cambridge, 1977) — the classic history.
Denis Diderot's Letter on the Blind (1749) is where the two-dimensional version of the question first appears — roughly fifty years after Locke

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#92 Molyneux's Problem and Questioning the Perception/Cognition Border — with philosophers Janet Levin and Brian Glenney

love & philosophy

#92 Molyneux's Problem and Questioning the Perception/Cognition Border — with philosophers Janet Levin and Brian Glenney