Nescience, cognitive closure, and the difference between a wall and a puzzle…
There is a gap in ordinary English that you generally only notice when you need it.
We have a rich vocabulary for not knowing things. *Ignorant*, *unaware*, *uninformed*, *clueless*, *in the dark*. But every one of these words carries a hidden assumption: that the thing not known is the sort of thing that *could* be known by the person not knowing it. Ignorance is a deficit against a standard. It implies a book unread, a lesson unlearned, a fact that was sitting there available. You can fix ignorance by handing someone a pamphlet.
What we lack is a common word for the other case – where the failure is not in the person’s diligence but in their equipment. Where the thing isn’t merely unknown but *unthinkable by that kind of mind*, in the way that a smell is unthinkable by a thermometer. Not a gap in the map, but a limit on what can be mapped at all.
This is not a merely lexical complaint. The word you reach for commits you to a claim about the world, and the claim is usually much stronger than you intended. So it is worth going slowly.
I. The available words, and what each one smuggles in
**Nescient** is the best single word. It comes from Latin *nescire*, to not-know, and it has been doing serious work in theology and epistemology for centuries. Its virtue is that it names a *condition* rather than a *failure*. To be nescient of something is not to have neglected it. Nescience is closer to a state of the organism than to a gap in its education. It is also usefully rare, which means it hasn’t been worn smooth by casual use the way *ignorant* has.
**Incognizant** is the plainer cousin – serviceable, slightly bureaucratic, and it drifts back towards ordinary unawareness. **Insensible to** is nicely physical, with a suggestion of sensory rather than intellectual failure, which may be exactly what you want. **Benighted** is archaic and faintly insulting; it implies a darkness that someone could have walked out of. **Oblivious** is the weakest of all – it means inattentive, and inattention is a moral failing in miniature, which is precisely the wrong note.
Then there is a second family of words, for a subtler thing: not the unawareness itself, but the unawareness *of* the unawareness. The recursive case. Because the truly closed-off mind does not experience itself as missing anything. It experiences the world as complete.
**Anosognosia** is the clinical term, coined by Babinski in 1914, for a patient’s unawareness of their own deficit – the stroke patient with a paralysed arm who sincerely reports that the arm is fine, and who will produce elaborate reasons why they simply don’t feel like moving it right now. It has escaped the clinic and is now used, sometimes loosely, for any blind spot about a blind spot. **Scotomised**, from *scotoma*, the blind spot in the visual field, does similar work with a psychoanalytic accent: a perceptual blankness where something intolerable ought to be. Freud was suspicious of the term and preferred to talk about disavowal, but *scotoma* has survived because the image is so good. Your own retinal blind spot does not appear to you as a hole. It appears as nothing at all, seamlessly filled in. You have to hunt for it with a card and a dot to prove it is there.
That is the phenomenology we are after. Not a hole in the world, but a world with no hole in it.
II. Cognitive closure
The philosophical term of art is **cognitive closure**, and it belongs to Colin McGinn, who set it out in a 1989 paper asking whether we can solve the mind-body problem. His answer was no, and his reason was structural rather than pessimistic.
Every mind has a range. A dog’s mind is well adapted to a rich world of scent, social hierarchy, and object permanence, and it is closed to arithmetic – not because dogs are stupid in a way that could be remedied with better schooling, but because the concept of a prime number is not a thing a canine cognitive system can form. The dog is not frustrated by this. There is no dog-shaped ache where mathematics should be.
McGinn’s move was to ask why we should assume our own range is complete. Our brains are organs shaped by selection pressures that had nothing to do with metaphysics. It would be a startling coincidence if the set of true things happened to line up exactly with the set of things a primate social-cognition engine can represent. Some truths may simply fall outside our range, and – this is the important part – we would have no way of detecting their absence. Our world would look complete, because it always does.
The position acquired the name **mysterianism**, coined half-jokingly by Owen Flanagan after the 1960s garage band ? and the Mysterians, and it has been fought over ever since. Daniel Dennett’s objection is the sharp one, and worth keeping in your pocket: an argument from cognitive closure is very hard to distinguish, from the inside, from a failure of imagination. “I cannot conceive how X could be explained” is a fact about you. Treating it as a fact about the universe requires an extra step that mysterianism has never quite managed to justify. Every hard problem looks closed until the week before it opens.
Hold onto that objection. It is going to matter later.
—
III. Umwelt: the sensory version
If you want the version with less metaphysics and more biology, the word is **Umwelt**, from the Baltic-German biologist Jakob von Uexküll, writing in the 1930s.
Uexküll’s insight was that an organism does not live in *the environment*. It lives in the environment *as constructible by its own sensory apparatus* – its Umwelt, its self-world. And these worlds are astonishingly narrow. His famous example is the tick, which lives in a world assembled from three cues: the smell of butyric acid, which tells it a mammal is passing beneath; a temperature of around 37 degrees, which tells it where to burrow; and the feel of hair, which tells it where not to. That is the whole world. There is no colour in it, no sound, no shape. A tick can wait years on a branch in a world made of three facts.
The great virtue of *Umwelt* is that it makes the point without any philosophical commitment at all. It is an empirical claim about sensory ecology. The tick is not being denied access to a richer reality by some Kantian veil; it simply has three receptors. And nothing in its world indicates that anything is missing.
If your interest is in intelligences with different bodies, *Umwelt* may be the more honest word than *cognitive closure*, because it locates the limit in the sensorium rather than in the intellect – and sensory limits are the kind of thing you can actually go and measure.
—
IV. The bat, and why it is not about bats…
The essay everyone eventually arrives at is Thomas Nagel’s “What Is It Like to Be a Bat?”, published in *The Philosophical Review* in 1974, and it is worth being precise about what it argues, because it is very frequently misremembered.
Nagel is not saying that bat echolocation is hard to imagine. He is not saying that we lack data about bats. Neurophysiologists know a great deal about the bat’s auditory cortex and can say in detail how the returning echo is processed into a representation of a moth’s position and velocity. The information is not the problem.
His claim is about the *structure of imagination*. When we try to imagine being a bat, what we actually do is imagine ourselves with modifications: ourselves, but hanging upside down; ourselves, but with a sonar sense grafted on. That is imagination working the only way it can, by extrapolation from our own case. But it delivers only what it is like *for us* to be bat-like. It cannot deliver what it is like for a bat to be a bat, because the extrapolation always starts from the wrong place. And there is no second method available.
So the barrier is not informational. It is not even, strictly, a barrier of intelligence. It is that the subjective character of experience is only available from a particular point of view, and the tool we use for occupying other points of view is a tool that works by dressing ourselves up.
This is why *nescience* and *cognitive closure* are the right register and *ignorance* is not. There is no pamphlet.
—
V. Four more words, for four different jobs
Once you are in this territory, several traditions offer terms that overlap without being synonyms. They are worth separating, because each carries a different diagnosis of *why* the thing is inaccessible.
**Noumenal** (Kant, 1781). The thing as it is in itself, as opposed to the thing as it appears. For Kant the barrier is not our species’ particular equipment but the very structure of experience: space, time, and the categories are the forms our intuition imposes in order to have experience at all, so they cannot also be read off as features of reality behind that experience. Use *noumenal* if you want the inaccessibility to be permanent and principled rather than contingent on our being primates. Note that this is a *stronger* claim than McGinn’s – a smarter alien would not do any better, because it would have its own forms of intuition.
**Radical alterity** (Levinas, *Totality and Infinity*, 1961, and after him a great deal of anthropology). Otherness that cannot be absorbed into the categories one already holds. Levinas’s point was ethical before it was epistemological: the failure to comprehend the Other is not a defect to be repaired but the very thing that makes the Other a claim on you rather than an object for you. If your interest is in what it would *mean* to encounter an intelligence you cannot model – rather than in whether you could model it – this is the vocabulary.
**Incommensurable** (Kuhn, 1962). No shared measure. Two frameworks fail to translate not because the dictionary is incomplete but because the terms are individuated differently at the root, so that agreement and disagreement both become ill-defined. Kuhn spent the rest of his career walking back the strongest readings of this, which is itself instructive: near-total incommensurability turns out to be hard to defend, and what survives is a claim about difficulty and loss in translation rather than impossibility.
**Apophatic** (Pseudo-Dionysius, and the *neti neti* – “not this, not this” – of the Upanishads). Not a description of the ignorance but of the *only available mode of speech* about it: saying exclusively what the thing is not. It is worth knowing that negative theology is the most developed technique humanity has ever built for talking at length about something held to be constitutively beyond conception. If you find yourself writing about an unimaginable mind, you will end up doing apophasis whether or not you have a name for it. Better to know you are doing it.
—
VI. Lem, or: the mirror is the only instrument we have
The novelist of this problem is ‘Stanisław Lem’, and he is more rigorous about it than most philosophers.
*Solaris* (1961) is usually described as a novel about an alien ocean. It is more accurately a novel about a library – the enormous, futile, century-old discipline of “Solaristics“, with its schools and schisms and competing taxonomies of the ocean’s formations, all of it elaborate and none of it contact. The ocean produces the visitors, apparently from the scientists’ own suppressed memories, and the humans cannot determine whether this is communication, experiment, cruelty, indifference, or a reflex with no more intent than a knee-jerk. The book’s cruelty is that it withholds even the certainty that there is even a question being asked.
*His Master’s Voice* (1968) does the same thing with a signal from space, which a team of the best minds available decodes into two substances of ambiguous properties and cannot get further, and cannot tell whether their partial success is genuine or a Rorschach blot. Lem’s recurring point, stated bluntly in both books, is that we do not go looking for other minds. We go looking for mirrors, and we call the mirror a discovery. Projection is not a mistake we could avoid with more discipline; it is the only instrument in the kit.
VII. Now the interesting part: chirality is not the case you think it is…
Here is where the argument gets useful, because there is a very natural example of “an intelligence I could never comprehend” that turns out, on inspection, to be a completely different kind of problem – and the difference is the whole lesson.
Suppose you propose two candidates for radically alien minds: a non-carbon intelligence, and a *mirror-image* intelligence, built from the enantiomers of our own biochemistry.
The first is a genuine Nagelian case, at least potentially. A different substrate might well support a different phenomenology, and we would have no method for checking, and no method for checking whether we had failed to check.
The second is not. Chirality is a fact about molecular geometry, not about experience. Terrestrial life is homochiral – we use left-handed amino acids and right-handed sugars, an asymmetry that is very likely a frozen accident from a chemistry that could have gone either way. A perfectly mirrored human being would be biochemically incompatible with us in interesting ways: they could not digest our food, our drugs would not fit their receptors, some of our smells would smell like something else to them. But they would not be *phenomenologically* alien. They would have your memories, your emotional range, your sense of humour. They would find your novels moving. There is no hard problem here, only a divergence & supply-chain problem.
So the mirror case is not a wall. What it is instead – and this is far more interesting – is a **communication** problem, and it has a name and a history.
VIII. The Ozma problem
Martin Gardner named it in *The Ambidextrous Universe* (1964), after Project Ozma, Frank Drake’s 1960 attempt to listen for interstellar signals at Green Bank, which Drake had named after the princess in Baum’s Oz books.
The problem is this. You are in radio contact with a civilisation somewhere distant. You share no objects. You can send only signals – that is, information, not things. You can establish a common vocabulary for numbers, for the elements, for the wavelength of a hydrogen transition, for anything you can define by its structure. Now: **communicate to them which of their hands is the left one.**

It seems, on first inspection, to be a perfect sealed impossibility. Every method you try fails. You cannot say “the hand on the same side as the heart”, because you cannot establish that their hearts are on the side ours are, and in any case you’d need to define “same side”, which is the thing you are trying to define. You cannot appeal to any geometrical description, because every geometrical description of a left hand is satisfied equally well by a right hand – that is what enantiomorphism *means*. You cannot appeal to astronomy, because they cannot tell whether they are looking at their sky or its mirror image. Every asymmetry you reach for turns out to be a convention or a local accident.
The Ozma problem looks exactly like cognitive closure. It has the right shape: the failure recurs at every attempt, and for what appears to be a principled reason rather than a contingent one.
And then it was solved. Not by philosophy – by an experiment.
In 1956, Tsung-Dao Lee and Chen Ning Yang pointed out that parity conservation, universally assumed, had never actually been tested for the weak nuclear interaction. In early 1957 Chien-Shiung Wu tested it, cooling cobalt-60 nuclei to near absolute zero and aligning their spins in a magnetic field. If parity held, the beta-decay electrons should have come out symmetrically with respect to the spin axis. They did not. They came out preferentially in one direction. The universe, at the level of the weak force, distinguishes left from right.
Which means the Ozma problem has an answer, and the answer is a recipe: *run this experiment, note which way the electrons go, and now we can both define “left” without ever pointing at anything.*
Gardner, being honest, flagged the remaining loophole in his own book: if your correspondents are made of antimatter, the recipe reverses, and you have merely traded the handedness ambiguity for a matter/antimatter ambiguity. That gap closed too. In 1964 Cronin and Fitch found CP violation in neutral kaon decay, which gives an absolute, convention-free distinction between matter and antimatter – and therefore, in principle, a fully unambiguous definition of “left” transmissible over a radio link to strangers.
The wall fell twice, in eight years, both times because someone went and looked at a nucleus.
IX. So: how do you tell a wall from a puzzle?
This is the thing worth taking away, (if you have read this far, well done, dear reader) and it is somewhat uncomfortable.
The Ozma problem *felt* closed. It had every hallmark: repeated failure, a structural-seeming reason for the failure, an air of “you cannot get there from here”. Sophisticated people spent decades treating handedness as the paradigm case of something communicable only ostensively – something you could only teach by pointing, never by describing. They were wrong, and the correction did not come from thinking harder about the problem. It came from an unrelated corner of physics noticing that a symmetry everyone had assumed was simply an untested assumption.
The bat may be different. Nagel’s argument has survived fifty years of attack in a way that most such arguments do not, and the reason is that it doesn’t rest on our failing to imagine a mechanism; it rests on a structural feature of how imagination works at all. But you should hold even that lightly, because Dennett’s objection stands: from the inside, a genuine wall and a puzzle you haven’t cracked look precisely identical. That is what it is to be nescient rather than ignorant. Nescience does not announce itself. There is no ache in the shape of the missing thing.
Which means the vocabulary carries a bet, and you should know which bet you are placing when you choose a word.
Say *ignorant* and you have claimed the thing is knowable and someone has slacked. Say *nescient* and you have claimed the not-knowing is a condition rather than a failure, without yet saying whether it is curable. Say *cognitively closed* and you have made a strong empirical claim about the architecture of a mind – a claim which, historically, has a poor track record. Say *noumenal* and you have made a metaphysical claim that no future experiment can touch, which is either admirable rigour or a way of insulating yourself from being proved wrong, depending on the day. Say *radical alterity* and you have changed the subject from knowledge to ethics, which is sometimes the right thing to do.
The most defensible position, and the least satisfying, is probably this: we can identify with confidence the cases where our imaginative method breaks down, and we cannot reliably tell which of those breakdowns are permanent. The honest word for the state is *nescient*. The honest posture is apophatic – say what it is not, and keep the account open. And the honest example to keep beside the bat is the Ozma problem, precisely because it is the one that got away.
—
Appendix: a working glossary
| Word | Use it when the emphasis is on… |
|—|—|
| **nescient** | not-knowing as a condition rather than a failure; no implication of blame |
| **incognizant** | plainer register; unawareness without the theological weight |
| **insensible to** | the failure is sensory rather than intellectual |
| **anosognosic** | unawareness of one’s own deficit; the recursive blind spot |
| **scotomised** | a blankness where something intolerable should be; psychoanalytic flavour |
| **cognitively closed** | a specific mind’s architecture cannot represent the concept (McGinn) |
| **outside its Umwelt** | the sensorium cannot construct the relevant world (Uexküll) |
| **noumenal** | inaccessible in principle to any experiencing subject (Kant) |
| **radical alterity** | otherness that resists absorption into existing categories (Levinas) |
| **incommensurable** | two frameworks with no shared measure (Kuhn) |
| **apophatic** | the mode of speech: only negations available |
| **ostensive** | learnable only by pointing – what Ozma was thought to be, and wasn’t |
—
Sources worth reading directly, & citations:
– Thomas Nagel, “What Is It Like to Be a Bat?”, *The Philosophical Review*, 1974
– Colin McGinn, “Can We Solve the Mind-Body Problem?”, *Mind*, 1989
– Jakob von Uexküll, *A Stroll Through the Worlds of Animals and Men*, 1934
– Martin Gardner, *The Ambidextrous Universe*, 1964
– Stanisław Lem, *Solaris* (1961) and *His Master’s Voice* (1968)
– C. S. Wu et al., “Experimental Test of Parity Conservation in Beta Decay”, *Physical Review*, 1957























