Blindness and Enlightenment: An Essay 
by Kate Tunstall.
Continuum, 238 pp., £17.99, August 2011, 978 1 4411 1932 2
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That, I suppose, must be my mother’s eye, up there on the monitor: that bobbing dark yolk, fringed by wriggling capillaries and the stainless steel of the speculum that holds her lids apart. I’m down the corridor from the operating theatre, waiting to drive her home with her patch and new lens. On the live action screen, I watch a scalpel take aim at her pupil and pierce the cornea at a point on its circumference, opening up for the instruments that will detach the cataracted lens, scrunch it to pieces and hoover the pieces away. After that moment when the metal first nicks the jelly, it’s all commandingly impersonal. The servicing of ‘the soft machine’ (as William Burroughs called the body) proceeds to anaesthetising muzak, and tomorrow or the next day my mother, only a little sore, will start to see the world again through her new synthetic lens. For me, there will just be a faint twinge, thinking how this keyhole to the soul, so deep and so watchful, can abruptly translate into a probed gelatinous mass, quivering like an egg as it fries.

Do they hook the monitor to the operating theatre to educate, or overawe, or amuse us, or what? Well, ‘the Eye, that most amazing, that stupendous, that comprehending, that incomprehensible, that miraculous Organ’, is always going to hold our attention: our psychology dictates as much. I don’t suppose the premises involved in this peculiar form of ‘theatre’ were either more or less confused in 18th-century Europe, when townspeople flocked to watch the oculists perform. John Taylor was the superstar of sight restoration, taking his show around England, Germany, Italy and France: many purblind celebrities would be subjected to his oratorical preambles (I quote from one above) before the scalpel plunged in. How far did Taylor’s ‘couching’ (i.e. stuffing the cataract away within the eyeball) serve the needs of the sight-deficient? It’s said that he managed to blind first Bach and then Handel. Even so, his reputation stands higher than that of Joseph Hillmer of Berlin, who travelled around pulling in patients with the promise of a treatment ‘that works in minutes’. A few days after he left town, a 19th-century historian reports, ‘almost all of them were inoperably blind.’ His surgery was performed in the days before anaesthetics. ‘When one woman shrieked in pain, he gave her a clip round the ear, when he already had his needle in her eye.’

Between Hillmer and the contemporary eye clinic stands the Enlightenment. By any construal, it stands for the development of a public arena, one in which impostors with presumptions to authority could be critically examined. The Enlightenment also implies progressive practical amelioration, delivering eventually anaesthetics and acrylic lenses. Equally, we might refer to it for the ancestry of that live-action monitor, that watching-machine. ‘The Enlightenment and the Revolution it helped spawn,’ Martin Jay wrote in Downcast Eyes, his historical survey of the rhetoric of vision, may ‘be justly said to have expressed that privileging of sight so often taken to characterise the modern era in general.’ By ‘so often taken’, he is referring to the impact of Foucault’s pessimistic interpretive schemes, which ascribe to the 18th century a belief in ‘bringing to light’ and ‘the open naivety of the gaze’ that would eventually deliver systems of surveillance. But immediately Jay qualifies that reading. Turn to some of the era’s seminal texts, he writes, and you see that such ‘visual primacy was by no means without its complications’. And he refers us to Diderot’s Letter on the Blind for the Use of Those Who Can See, written in 1749.

This Letter has now been translated for the first time in more than two centuries by Kate Tunstall, who accompanies it with a stylish and subtle interpretive essay. It was written when Diderot was 35 and had only recently embarked on the Encyclopédie. He was hardly out of the Parisian equivalent of Grub Street: a sanguine, voluble struggler who had spent several years supplying maths tuition, off-the-peg sermons, pornography and translations from English to feed his wife and children. Voltaire, almost a generation older, was standing by now on a plateau of distinction: beyond it, peaks in the distance, rose the writings of Locke and ‘Neuton’, the Englishmen Voltaire revered. Diderot had taken a step towards this level three years earlier when he published his breezily sceptical Philosophical Thoughts: ‘criminal opinions’, in the judgment of the Paris Parlement, which ordered the volume to be publicly burned. Now, in 1749, Diderot snatched at a topical gambit. The dubious Hillmer had turned up in Paris and had been invited by René Réaumur, the head of the Académie Royale des Sciences, to conduct a cataract-couching on a woman who had been born blind. In response to ‘all the observations people are constantly making ever since the Prussian arrived’, Diderot would try to pitch in on the discussion.

What was its point? Back in 1688, Locke, developing his theory of how the ‘white paper’ of the mind is painted with ‘all the materials of reason and knowledge’ by experience alone, had been set a question by an Irish friend called William Molyneux. Say a man born blind is well acquainted with two distinct tactile experiences, one of a metal cube and the other of a metal sphere, both equal in size. Someone cures his condition and for the first time he has visual experiences of two differing shapes. Will he immediately know which is which? How can he, if the paper of the mind is truly blank and there is no innate structure of ideas within which to co-ordinate the sense data we receive from separate inputs? So Locke reckoned, in defiance of both ‘common sense’ – as we call our intuitive expectations these days – and of the sensus communis, the concept, running from Aristotle to Descartes, of a central mental junction box.

If the man cured of blindness had no option but to reach out and check the objects’ identity with his fingers: if concepts of form, and of all that more generally might depend on them, could only be built piecemeal from the bottom up, then that might help to legitimate other types of bottom-up organisation. Diderot’s philosopher friend the Abbé de Condillac had taken up Molyneux’s Question in 1746 – his interest in it ran in parallel with his interest in progressivist economics and politics. Put the question to the test, then: bring together a suitable oculist, a suitable patient and suitable objects of sense-experience, and as soon as the cataracts are cut away and light reaches the brain, decide which is the more scientifically tenable, the Cartesian rationalism of absolutist France or the Lockean empiricism of constitutionalist England.

Did such a moment of truth arrive when Hillmer took his scalpel to a noble blindwoman under Réaumur’s supervision? We have no record of that. (And we might doubt that it could have.) All we know is that, launching into his own conversational foray, Diderot made a show of refusing the whole question. You can forget about that pompous Réaumur, who wouldn’t admit me to observe his experiment – so his Letter effectively begins – because I’ve just been to talk to a blind man who will make you reconsider all your preconceptions regarding eyesight and touch. And he begins a giddy, flamboyant sideways dance, for digressing ‘is the very nature of our treatise,’ as he admits towards its conclusion, some forty pages later. ‘You must be kind enough to allow me all these digressions, for I promised you a conversation, and I can’t keep my promise unless you allow me this indulgence.’ ‘You’, here, being ‘Madame’, the letter’s otherwise anonymous addressee. The writer is keen to flatter her literary taste and philosophical curiosity. He allows us to think he might know her rather well, slipping in asides about times spent together and memories of intimate sensation. He allows us, Tunstall notes, to conceive of her as Madeleine de Puisieux, an intellectual with whom Diderot had been conducting an affair.

The faint erotic friskiness and repeated twists and turns of the discussion bring it close to the mid-18th-century vogue of ‘rocaille’ (later dubbed ‘rococo’): the aesthetic of designers such as Meissonier, centrifugal and deliriously complex. Another comparison would be with Tristram Shandy, a book Diderot immediately fell in love with. The craziest section of the Letter is an account of a calculating machine for the blind, a gridded pinboard whose operations are set out in five large diagrams. ‘You would find it very useful should you ever fancy feeling your way through some long calculations,’ Diderot tells Madame, with satirical implausibility. (Tunstall wonders whether his swapping ‘left’ for ‘right’ in the textual explanation is deliberately nonsensical.) At the same time usefulness is a value dyed deep in Diderot’s mental fabric – witness the Encyclopédie itself, that diagram-stacked monument to artisanal know-how, to mechanical robustness, our primary evidence for supposing that the Enlightenment had to do with practical amelioration. It’s just that in 1749, usefulness and playfulness could coexist, in a way it’s since been rather hard to recapture.

Tunstall, poring over the text, finds an inner consistency in its ‘reflections, reversals and refractions’: they all, she argues, point back to its concern with optical issues and hence with mirroring. And it’s true that, unlike Tristram Shandy, the Letter does close around a definite subject. It presents two case-studies of blind men – each, though freely embroidered, possessing a factual basis. The first, Diderot’s recent interviewee, is a canny, pleasure-loving provincial bourgeois renowned for the liqueurs he concocts. The other, ten years deceased, is Nicholas Saunderson, the calculator’s inventor, a successor to Newton as professor of mathematics at Cambridge. The two, Tunstall writes, ‘are clearly set up to echo one another’. Each mocks any assumptions of the superiority of the sighted. Saunderson lectures his students as if they were the ones who were blind, while ‘the man-born-blind of Puiseaux’, when asked what he understands by vision, answers Diderot with formulations as precise as those of Descartes. Precise and a little bizarre: he calls eyes ‘organs … affected by the air the same way as my hands are affected by my stick’. Yes, the blind to us sighted are strange. But that’s an effect of perspective: so much is the text’s repeated refrain. (Tunstall notes some affinity to the cultural-relativist badinage of the era, in texts such as Montesquieu’s Lettres persanes.) On top of that, Diderot can’t resist playing the blind for comedy. The pleasure-lover, with his superior awareness of skin textures, would have ‘no reason to fear that he might mistake his wife for another woman, unless he stood to gain by it’. And at the same time he plays them hard for pathos too.

He runs through the intellectual achievements of Saunderson – there’s more mischievous juggling in the way Diderot insinuates at one point that the blind are natural adherents to Berkeleian idealism, and at another, that they’re fated to Hobbesian materialism, and that arguably, therefore, each philosophy in turn is in a bad way ‘blind’ – and then the prose comes to a sort of caesura. I seem to hear (not that the methodologically scrupulous Tunstall would dream of asking me to) the writer returning to his manuscript one bright morning and – exclaiming ‘Why the hell not!’ – setting out to invent a death speech for Saunderson. It’s delivered to a vicar who, wanting the mathematician to die a Christian, recites the argument from design – consider God’s marvellous creation etc. ‘That beautiful great spectacle,’ Diderot’s Saunderson begins, ‘was never made for me! I have been condemned to live my life in darkness.’ And he launches into an alternative cosmic vision, one of all-enveloping chaos and contingency, within which order and beauty are but transitory tricks of the light, his own imperfect senses being representative of its many ‘monstrous outcomes’: ‘Oh, philosophers!’ he exclaims. ‘Come with me to the edge of this universe, beyond the point where I can feel and you can see organised beings; wander across that new ocean with its irregular and turbulent movements and see if you can find in them any trace of that intelligent being whose wisdom you admire here.’ The peroration gathers to a dark swirling roll – the one passage of the Letter no reader would ever forget – and crashes on the mathematician’s last words, which, with a paradoxical pathos, reach out to his predecessors’ deity: ‘Oh God of Clarke and Newton, take pity on me!

Why the hell not? Well, the Letter went on sale in June; within a week, Diderot received a letter of praise from Voltaire – ‘one of the sweetest moments of my life’ – and at 7.30 a.m. on 24 July, the police marched into his second-floor apartment. At court in Versailles, the Comte d’Argenson was keen to show muscle by rounding up anyone who wrote disobligingly of his protector Mme de Pompadour, the widely disliked mistress of Louis XV. One Latin Quarter verse squib had been discovered inside a copy of the Letter, and moreover, Joseph d’Hémery, the police inspector of books, had Diderot marked down as ‘a very clever boy but extremely dangerous’: a biggish fish, then, to add to the haul. Diderot, banged up six miles outside Paris, wasn’t too sure whom he’d offended – could it have been Réaumur’s blind VIP? He at first disclaimed authorship (after all the Letter, supposedly published ‘à Londres’, was simply signed ‘***’), but after two months he wrote to the chief of police promising that this text and the Philosophical Thoughts would be the last of his ‘mental intemperances’ and offering to shop his printers. Meanwhile, the people who’d hired him to produce the Encyclopédie and Mme de Pompadour’s friend Voltaire had been piling on pressure in all the right places. Come November, Diderot at last got back home to his desk.

From this turn of events in 1749, many historians have liked to trace the beginnings of an oppositional nexus, linked to the Encyclopédie, that would gather momentum until the great eruption forty years later. Tunstall is none too keen to join them. ‘It is important,’ she writes, ‘to resist reading the Letter in a proleptic light,’ for ‘hindsight blinds us to the text’s ironies, tempts us into resolving its ambiguities and thereby obstructs or, at least, seriously impoverishes our reading.’ Instead, she persuasively involves us in the frames of reference that would have been alive for Diderot, cutting off at the point when his text was printed. And yet the details of his subsequent brush with the law, petty and unheroic as they are, bear out the drift of her reading. It seems that neither Diderot nor those who detained him had any distinct idea that the Letter was an atheist manifesto, the kind of argumentative missile it would later be taken for. Its fascinated but disrespectful probings into idealism and materialism, its poetic invocation of a ‘blind’ and purposeless universe, capped by the drama of a dying man’s appeal to God: all these were strands interweaving in a rococo fantasia of the intellect that, thanks to some squabble at court, got accidentally rerouted onto the road to revolution.

I think Tunstall gets one step too involved in the playfulness of the Letter. She has decided that in her own essay its writer cannot be named Diderot, but must be represented only by his literal printed signature – by ‘the paradoxical inky glimmer of three little stars’. My eyes kept stumbling on this ***: this symbol that had no sonic referent, unless I was laboriously to mouth it as Astérix. Was Tunstall trying to bring home how hard it is to rely on just one unsupported sense? But her fancy manoeuvre entails too much fastidiousness about authorship. Sure, the persona in the textual conversation is not exactly the harried family man living in the second-floor apartment, but why should ‘Denis Diderot’ be closed down as one thing only? Certain writers – Fernando Pessoa, for instance, with all his aliases – have been truly intent on slicing up their identity. But most of the rest are a little blurry, a little multiple and overlapping. Listen to Tunstall herself in her conclusion, archly sidling up to someone very like Diderot, just as the author’s persona sidles up to someone very like Madeleine de Puisieux: ‘As a participant in this game of nods and winks, nudges and whispers, the reader has been enjoying supplying half the ideas and half the words for herself. She has taken her place in the … conversation.’

But what happened in that game to Molyneux and his question? What did Diderot contribute to the 18th-century conversation about the way sight relates to touch, and whether behind the two there lies a single reasoning, co-ordinating mind? When at last he does get round to the issue, his approach is gradualist, steady and undramatic. You can’t expect someone born blind and given sight instantly to deliver a meaningful judgment as to the identities of two objects, he tells us – or if you really require one, you must train him up first. For ‘experience alone … teaches us to compare sensations with what occasions them.’ Reason does not so much lie behind our sense impressions as slowly erect itself on them. It is not sight per se that Diderot’s version of the Enlightenment privileges, pace Foucault, but education.

Does that settle the Irish savant’s problem? It hasn’t gone away. During the past ten years, MIT researchers led by Pawan Sinha applied it to a group of Indian children treated for cataracts. When these children were given items first as objects to feel and then to identify by sight, their initial matches could as well have been guesswork. No ‘cross-modal representation’, in the researchers’ words, no sensus communis, could be seen in action: the brain’s paper looked blank. And yet within a time far shorter than any scientist would have predicted, correct identifications were established. There you have it, Molyneux: ‘Initially no but subsequently yes,’ Sinha says. There are certain latencies, it seems, that the brain does possess.

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