Diderot doesn't strictly speaking theorize Beauty. He encounters different models, he measures himself against different discourses on the Beautiful¹.

First of all, there's the Beautiful understood as wonder of the world; articulated with the Good, it offers itself to the subject as a spectacle of the world and nature and determines belief in God, creator of the best of all possible worlds; this conception is, so to speak, distanced from the outset by Diderot². But the marvel never remains far away, always ready to make a comeback, to offer the pleasure of a contrast, the vertigo of a superposition with the uglinesses of what, really, is given to see.

Then comes Beauty understood as relation³, first and foremost an internal relation, i.e. the harmony and consonance of parts ordered in relation to a whole (we're still very close to Beauty as wonder), then an external, mimetic relationship, from the thing imitated to its imitation: the Beautiful then becomes technicized and can just as easily qualify the representation of an ugly thing, a well imitated ugliness.

Then emerges the disturbing idea of an instability and fundamental reversibility of the Beautiful⁴. Diderot articulates this reversibility in a Platonic-inspired discourse, where the Beautiful is understood as ideal model of beauty, i.e. as an abstract, absent image, both foreign to reality and alien to technique, as fantasma, both ghost and representation, from which the artist works⁵. This is Diderot's most original theoretical development. This dialogue between the artist and the ghost, the fantasma of representation, then highlights not the reversibility, but the monstrosity of Beauty, which contact with reality exposes and distorts, which representation undoes by shaping it.

However, in piecing together these discourses on the Beautiful, we feel that we're missing what constituted Diderot's essential contribution to the question of the Beautiful. Beauty takes us beyond modeling. The aesthetic question opened up by the Beautiful no longer grasps it as the object of a treatise on universals, but as the symptom of a logical flaw, a point at which discourse and even thought skid, flabbergasted, carried away to something else. Beauty then becomes the unrepresentable foundation of representation. Aesthetic jouissance, because it proceeds from this foundation, cannot therefore be the object of a discourse, or even of another discourse; it precisely opens up a silence and a confusion, it has to do with fantasy, with the haunting of a feminine truth of jouissance, a truth grasped in what constitutes it scandalous, incomprehensible, for what pleasure and knowledge confounded therein make the economy, if not of language, at least of its rhetorical articulation.

As soon as it is no longer the subject of a discourse, of a treatise, but arises one might think accidentally, in fact rather symptomatically, the aesthetic question is the object of a double detour: firstly, the demystification of the geometrical model of vision lays the foundations of philosophical materialism; secondly, in a more general, more encompassing way, the challenge of representing feminine jouissance opens up to subversive writing. At the very least, we will show that this double detour constitutes the major challenge of the Lettre sur les aveugles.

I. The Beautiful as negation of the visible

Negations

The text of the Lettre sur les aveugles opens with a negation, or rather a series of negations. To account for what it is to apprehend the visible, we would have to observe and analyze what it is like for the born-blind man who suddenly regains his sight. But, writes Diderot,

"I suspected well, Madame, that the born-blind man to whom M. de Reaumur has just had his cataract removed, would not teach you what you wanted to know" (DPV IV 17, 1st sentence of the Lettre).

M. de Réaumur, who operated on the demoiselle Simoneau, did not allow Diderot or his interlocutor to whom the Letter is addressed to attend the operation. The spectacle, the experience were therefore not seen, the first negation of vision, the first lack for the text, the first flaw for thought. The operation itself, the restoration of vision through the cutting of the scalpel, consists in the abolition of a negation, the subtraction of a subtraction. It's like a second-degree subtraction. Finally, Diderot's formulation suggests that the disappointment would have been the same in front of the spectacle Réaumur refused them, a spectacle where "I saw nothing to gain for my instruction nor for yours": a third negation is at play here, a kind of foundational subtraction that links the blind to something incomprehensible in vision. This third negation was brought to the fore on the very first page of the book, albeit cryptically: the Letter in fact bears in exergue a distorted quotation from Virgil, Possunt, nec posse videntur, "they can and they seem not to be able". We're probably to understand that the blind, who appear unable to see, in fact turn out to be quite capable of circumventing their handicap. Diderot in fact expands throughout the Lettre on the prowess of the various exceptional blind people he has met or heard of.

Nec posse videntur, literally means "they are not seen power". They are not seen, the third negation of sight. The circle of the blind widens: the blind do not see; philosophers do not see the blind suddenly see, thanks to surgery; humanity as a whole finally does not see that the blind have always seen.

Virgil had in fact written, in Canto V of the Eneid, about a boat race, possunt quia posse videntur, "they can [win the race] because they believe they can [win it]". The hijacking of the Virgilian reference is underlined by the typographical change: nec is in roman in an italicized quotation. "They believe", another meaning of videntur, clearly marks that in his hijacking of the Virgilian formula Diderot, by bringing videri croire back to videri paraître, has revived, brought closer the etymological meaning of the verb, to be seen. Quia became nec, negation the focal point of a detour fraught with consequences. Quia is the logical sequence of causes, constitutive of the discourse; nec is the visual opposition of opposites, which founds the device. This too must be read as something other than discourse. On the one hand, possunt nec posse, this reversal of impotence into power through the pivot of negation; on the other videntur, passivated vision, vision of something suffered.

So, at the beginning, there are three negations. Negation of the framework of the experiment, Diderot and his interlocutor do not see the blind man; negation of the field of the experiment, the blind men eventually discussed in the Letter, not having undergone cataract surgery, are blind men who do not see and continue not to see ; finally, in exergue, negation of what is at stake in the experience, the blind are not seen to be able to see, and yet are not without seeing; the very boundaries of the field of the visible are denied.

Supplements

The text confronts, so to speak, from the outset a depression, a series of subtractions, which it compensates for with a series of displacements. A logic of supplement is put in place. In the first place, Réaumur's operation has not been seen, but the text of the Lettre will make up for it:

"Que je serais heureux, si le récit d'un de nos entretiens pouvait me tenir lieu auprès de vous du spectacle que je vous avais trop légèrement promis!" (P. 17.)

Secondly, the blind people the Letter will focus on have not been operated on, but touch and hearing make up for their failing eyes, so they don't ask to see. The blind man from Puiseaux is very clear on this subject:

"It would therefore be worth as much to perfect in me the organ I have, as to grant me the one I lack." (P. 23.)

A telescopic arm would be preferable to the acquisition of a new meaning: the logic of the supplement refuses any epistemological leap.

Finally, in the third place, the scopic dimension of the visible escapes the blind, but Cartesian dioptric supplements this irreducibility with geometry.

Each of these supplements, in the text, in the sensitive experience and in its modeling, induces a displacement that constitutes a device. The "narrative [of] interviews", in its apparent disorder⁶, disposes the reflections and experiments that replace the failed spectacle of the operation and above all Réaumur's speech demonstratively ordering his observations⁷ : witness the late "Additions" to the Lettre, which complete the device. The blind man's tact, his manipulations, establish in a purely mathematical and abstract space⁸, in the very space of Cartesian Dioptrics, the disposition of objects meticulously arranged, ordered⁹. Finally, "Saunderson's machine" (p. 36), invented for calculus and geometry, consists of placing¹⁰ "on the gridded table" provided for the purpose, nails with small and large heads, whose distribution in space makes sense. Unlike our Arabic numerals, which are based on a differential system that individualizes different shapes, Saunderson's nails are of only two kinds: only their arrangement in space, only their respective places make sense¹¹.

The additions and subtractions that punctuate both the content and the enunciation of the Lettre are therefore not content to establish a balance, to account for a system of compensations, of equivalences between seeing and saying, between vision and geometry, between the visible and the differential play of the signifier. The logic of the supplement operates a displacement. The starting point is a game of plus and minus; caught between the double cut of the missing eyes and the collapsed cataract, the blind man represents this game. But the blind man is not only the one who cannot see. Videntur, he is the one who is seen, and by this he makes us see something else.

This other way of seeing first manifests itself in the blind man's difficult relationship to language¹². What is a mirror for the blind? What are eyes? What is physiognomy (p. 26)? Language is not only taken to task for rendering account of realities foreign to the blind. The blind man bypasses this liminal subtraction, proposes his definition and arouses embarrassed admiration¹³. His ingenious definitions are not wrong per se, or at least they are not more wrong than the expected definitions of the seer. But they are caricatures. They strip away the agreed-upon mechanics of what language models, and make conspicuous another dimension of reality, ignored by geometrical modeling.

From relief to device

By the relief provided by the mirror¹⁴, by the pressure of the air on the eye¹⁵, when confronted with the limits of his definitions, when he no longer understands, the blind man points out what, in this device, escapes geometric reduction. The question of relief blurs the reference points of Cartesian dioptric: a mirror gives the illusion of relief; a trompe-l'œil perspective produces the same illusion. However, neither the mirror nor the trompe-l'œil are shaped according to the relief they mechanically transmit to the eye. If the effect of the image on the eye is the same as that of the blind man's stick on his hand, how can we explain this relief that appears out of nowhere?

It's that in space something in the visible suddenly takes on relief out of nothing, something that the eye has no control over, something that starts from the object looked at, that returns to vision in an uncontrolled, as it were incomprehensible way¹⁶. This is about much more than relief. The poetic and epistemological stakes of the Lettre sur les aveugles, the passage to the device, take shape here: the device of the text, which is not Réaumur's speech but this interview or series of seemingly disjointed interviews; the device of Diderot's confrontations with the blind, not the linear unfolding of a surgical operation, but the unforeseeable conjuncture and reversals of a gripping face-to-face encounter; and finally, the devices imagined in space by the blind man, highlighting the limits of Cartesian dioptric. The device defeats the primitive logic of the Letter, this logic of the supplement for which it substitutes a second logic, based on the return effect in the device.

In fact, at the heart of the subtractions and additions set up within the logic of the supplement appears what can in no way be supplanted. Vision gives rise to a return effect around something the blind person cannot conceptualize, around an incomprehensible pivot that becomes a symptom. This blind spot for the blind man has to do with Beauty.

Beauty as symptom

The Beautiful is precisely what, in the visible, makes a symptom. The Dioptrics that makes us see with sticks does not account for the Beautiful:

"By dint of studying through tact the arrangement we require between the parts that make up a whole, in order to call it beautiful, a blind man manages to make a just application of this term. But when he says, this is beautiful, he's not judging, he's only reporting the judgment of those who see: and what else do three-quarters of those who decide about a play, after hearing it, or a book after reading it, do? Beauty for the blind is just a word, when separated from utility; and with one organ less, how many things whose utility escapes him? How many admirable things are lost to them! The only good that compensates them for this loss is to have ideas of beauty that are, to be sure, less extensive, but clearer than those of clear-sighted philosophers who have dealt with it at great length". (DPV IV 19.)

Here again, Diderot places a faulty experience at the start of the analysis: the blind man who seeks to conceive the beautiful shifts, as is his wont whenever he is confronted with visible data, what belongs to the eye to what his hand is capable of apprehending through tact. The lost spectacle of "admirable things" is compensated for by the study of "the arrangement" of the "parts that make up a whole", and in this arrangement, by the search for symmetries.

The blind man thus proceeds, of necessity, to a geometralization of the visible that forms the basis of Cartesian dioptrics:

"Madame, open Descartes' Dioptrique, and you will see the phenomena of sight related to those of touch, and optics boards full of figures of men busy seeing with sticks. Descartes and all those who have come since, have not been able to give us clearer ideas of vision; and this great philosopher has had no more advantage in this respect over our blind, than the people who have eyes." (P. 21.)

The blind man's failure points to the theoretical failure of Dioptrics. The blind man, if he succeeds in circumscribing a kind of external, social convention of the Beautiful, does not experience the intimate feeling of the Beautiful. Aesthetic emotion, in its irreducibility to the geometrical arrangement of forms, but also to the functional utility of objects, remains incomprehensible and inaccessible to him. The blind man compensates, makes up for it, "compensates for this loss" by excelling in what he has left. But the best of the eye is lost to him, that sensitive experience of the Beautiful that no discourse models.

II. Poetics of reversion, interlacing the gaze

The logic of the supplement here marks its limits and gives way to a second spring of the text, based on pivoting, reversibility, reversal. From the "arrangement" of objects, we move on to the device of vision, based on the to-and-fro of the eye and the gaze: the eye that rests on the object responds to the gaze that returns from the object; it looks at me, it shows. This phenomenon of return, from what is looked at to the eye that looks at it, is inaccessible to the blind. But the blind, through their incomprehension, point to its existence. Through the blind, Diderot highlights the monstration of the visible, which manifests to the eye the Beautiful insofar as it comes under the heading of "it shows", insofar as it is a phenomenon of return, insofar as it is the formless around which, in vision, it turns.

We need to take into account all the levels of the text where this reversion is played out. First, there's the Diderotian writing of the chiasmus, which turns terms inside out and undoes supplements; through the chiasmus, discourse enters a logic of the visible. In so doing, the chiasmus makes the experience miss.

Then it's the experience's misses, this passage to the blind man's point of view that blinds the question of point of view and brings to the surface, beyond modelizing discourses, not only the scopic irreducibility of the visible, but jointly with it the brutality of the real.

This reversal of the real constitutes the third level of the text, the most radical in its stakes and implications: it is the moment of the blind man's revolt, of his face-to-face confrontation with the law, the law of men and the law of God, which he denies and defies with all his might.

Chiasms

Diderot's predilection for the chiasmus has long been noted, not only as a characteristic of Diderot's style, but as the very form of his dialogic thinking¹⁷. Chiasmus is the basic structure of writing's transition from a discursive logic to a device logic. Here are a few examples. The blurring of the definitions of the blind man confronted on the one hand with the flat surface of the mirror, and on the other with the illusion of depth given by the trompe-l'oeil painting gives rise to the following formulation:

"he was tempted to believe that, as the mirror painted the objects, the painter in order to represent them, perhaps painted a mirror." (P. 22.)

The chiasmus, which inverts the phrase "la glace peignant" ("the ice painting") into "peignait une glace" ("painted an ice"), depicts the return effect of vision, but depicts it from the point of view of the blind man, i.e. in the vertigo of an incomprehensible formulation. The sentence escapes the logic of linear development, since the chiasmus forces us to visualize it in space, as a superposition, a crossing of terms. In this way, the text materializes as the edge of the visible. This incomprehensible pivot is captured in the chiasm's trap, around which vision returns to manifest beauty, in this case the beauty of painting first grasped as vertigo in the face of the illusion of depth.

Even when it seems not to deal with vision at all, the chiasmus gives an account of this same phenomenological irreducibility around which the return-effect occurs, and of which the scopic dimension is only one of the manifestations. The comparison of the blind with the sighted, for example, is superimposed on the comparison of animals, deprived of reason, with man, a reasonable animal. Just as the born blind man does not desire sight as a faculty superior to all those he otherwise possesses and has developed as a function of his handicap¹⁸, there is no reason why animals should be convinced of man's superiority on the pretext that reason would be a faculty superior to their various attributes. Diderot formulates this point of view as follows:

"all animals, willingly granting us a reason with which we would have great need of their instinct, will claim to be endowed with an instinct with which they do very well without our reason" (p. 23).

The chiasmus produced by the interchanging of the words "reason" and "instinct" represents the reversal of point of view, the taking of the floor in the face-to-face of those to whom the floor was not to be given, of these Others, animals or blind, struck by the subtraction and returning precisely this subtraction to the other camp, ours. The chiasmus thus represents the return effect of what is seen, the pivoting of the videntur around the negation of a lack, through the passage from "we would be in great need of" to "they do very well without". What is seen and returned is the instinct of animals: instinct was seen as a defect of reason, as pure subtraction; it returns as the prerogative of animals, as what we lack. Instinct is what escapes the geometrical modelling of reason; its irreducibility is of the same order as the scopic irreducibility of which beauty is the symptom.

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In the shift from the first chiasmus to the second, from the relief of ice to the instinct of animals, the Diderotian detour of the aesthetic question takes shape, and, through it, the fundamental issue at stake in the Lettre sur les aveugles: the question of the Beautiful, marking the limit of Cartesian discourse, its geometrical modelizations and its logic of the supplement, opens the philosophical conversation to the device, a device founded on the reversal in the face-to-face. A whole economy of revolt is then set in motion in the text, whose stakes are no longer the sole definition of the Beautiful, or of the visible, but the very representation of the world in its relationship with the law.

We'll have understood that the revolt against traditional, socially accepted and instituted representations of the world was aimed first and foremost at Descartes. The first illustrated plate in the Lettre is entitled "Figure from Descartes' Dioptrique" and depicts a blindfolded man holding two sticks in his hands. It comes opposite the following text from the Lettre, which we have already quoted:

"Madame, open Descartes's Dioptrique, and you will see there the phenomena of sight related to those of touch, and optical plates full of figures of men busy seeing with sticks." (P. 21.)

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The relationship between text and image is not obvious. In principle, it's not with two, but with one stick, much longer, that the blind make up for the failure of their eyes. But the small sticks in the picture don't touch the ground or any object: this has nothing to do with the white cane; these sticks aren't trying to see an object.

On the other hand, they are crossed. How can we not find here the figure of the chiasm, taken here in its properly phenomenological dimension of the figuration of vision, of what M. Merleau-Ponty designates as the intertwining of the eye and the gaze? Let's go back to the Dioptrique (1637). The plates there are not "full of figures of men busy seeing with sticks¹⁹". The Diderotian exaggeration conceals a precise reference to the sixth discourse, entitled "De la vision", where a figure represents a blind man holding a stick in each hand. Beyond point E, where the two sticks cross, their continuity is shown only by dotted lines. Reading the text sheds light on the meaning of these dotted lines: the Cartesian blind man's sticks are, in fact, virtual sticks materializing guiding lines, axes constituting a reference point in space. Descartes begins by explaining the relationship between vision and touch:

.

"For the situation, i.e. the side towards which each part of the object is laid with respect to our body, we do not perceive it otherwise through the intermediary of our eyes than through that of our hands" (p. 704).

In other words, to locate an object in space, our eyes proceed, like our hands, by relating the position of our body to the position of the object. Descartes describes this relationship in the following way:

"As, when the blind man, of whom we have already spoken so much above, turns his hand A towards E, or C also towards E, the nerves inserted in this hand cause a certain change in his brain which gives means to his soul to know, not only the place A or C, but also all the others which are in the straight line AE or CE, so that it can carry its attention up to the objects B and D, and determine the places where they are, without knowing for that nor thinking in any way of those where its two hands are. And so, when our eye or our head turns to some side, our soul is warned of it by the change that the nerves inserted in the muscles, which serve for these movements, cause in our brain." (P. 705.)

The blind man therefore uses his hands as abscissa (AE) and ordinate (CE) axes from which to determine the coordinates of an object B or D in space. The sticks materialize these axes. According to Descartes, the eyes proceed in the same way, but abstractly, each of the two eyes constituting for the brain respectively an abscissa axis and an ordinate axis. Note that the blind Cartesian, like the sighted one, shifts their axes in relation to objects so as to use only the abscissa, or only the ordinate, allowing Descartes, despite the awkward presence of both eyes, to reduce the space of vision to a line and evacuate the return effect of vision:

.

"The vision of distance does not depend, any more than that of situation, on any images sent from objects, but, first of all, on the figure of the body of the eye" (pp. 705-706).

Identified initially as a problem of localization in space, vision is thus placed under the control of the brain, which models shapes and distances from the eye's own fundus shape. Vision is active; it only takes place in one direction, and can only be conceived of as totally controlled by the subject looking.

What Diderot introduces, right from the exergue of the Lettre as we've seen, is the passivation of the videntur, that dimension of the visible that escapes the mastery of the intellect. The two crossed sticks of the Diderotian blind man become, in this new context, incomprehensible. Full sticks to the end, they open up to no virtuality, no abstract modeling. Deprived of points A, B, C, etc., they no longer geometrize any space, contenting themselves with figuring the irreducible presence of this crossing through which something returns.

.

Revolts

Blind Saunderson's rebellious speech is prepared by a youthful quarrel between the blind man from Puiseaux and one of his brothers:

"Impatient with the unpleasant words he endured from them, he seized the first object that fell to his hand, threw it at him, hit him in the middle of the forehead, and laid him on the ground.
This adventure, and a few others, led him to call the police. The outward signs of power that affect us so keenly do not impose them on the blind. Ours appeared before the magistrate, as before his fellow man. He was not intimidated by threats. What will you do to me," he said to Mr. Herault, "I'll throw you into a pit," replied the magistrate. - Eh, Monsieur," replied the blind man, "I've been there for twenty-five years." (P. 24.)

Unwittingly for his brother, the object thrown at him by the blind man hits the mark, as "notre aveugle adresse au bruit" (our blind man addresses the noise); as for the reply hurled at Hérault de Vaucresson, the terrible police lieutenant who is a great destroyer of Jansenists and convulsionaries, it hits the nail on the head. The face-to-face encounter with the blind man takes an unexpected turn.

This brutality of object and retort erupts at the heart of reversion as a barbaric dimension of man, irreducible to Cartesian rationality. In the outraged blind man, it is the wounded beast that responds. In this text, which never yields to self-pity for infirmities, the cry that arouses from the pain of living with disability is turned into heroic bravado. Diderot concludes the anecdote:

"We come out of life, as out of an enchanting spectacle; the blind man comes out of it as out of a dungeon: if we have more pleasure in living than he does, agree that he has far less regret in dying."

What the blind man lacks is beauty understood as the wonder of the world, the "enchanting spectacle" which for him is reduced to a dungeon. What we have before our eyes, and which is of the order of enjoyment, of a continuous enjoyment identified with the desire and happiness of living, this sensitive, intimate, daily experience of the visible beauty of the world is withdrawn from him.

The blind man doesn't care whether or not he sees objects with his eyes. What he really lacks is the enjoyment of vision, the deprivation of the "enchanting spectacle". More explicitly, Saunderson concludes as he dies: "I renounce without pain a life which has been for me only a long desire, and only a continual privation." (P. 54.)

Yet here again, things turn on their head. The lack of jouissance opens the blind man to philosophical detachment. Nothing holds him back, nothing offends him. The defect of beauty opens to the truth of the world.

Diderot advances very gradually on this terrain. He begins by suggesting that the subtraction of vision has metaphysical and moral consequences for the blind, on which it would perhaps be better to throw the veil:

"Our metaphysics do not accord any better with theirs. How many principles for them that are mere nonsense for us, and vice versa. I could go into detail on this, which would no doubt amuse you, but which certain people who see crime in everything would not fail to accuse of irreligion; as if it depended on me to make the blind see things differently than they do. I will content myself with observing one thing, which I think everyone must agree on; that is, that this great reasoning we draw from the wonders of nature, is very weak for the blind." (P. 28.)

At the heart of metaphysical subversion, it is indeed the absence of the Beautiful understood as the wonder of the world that does its work. The subtraction of the Beautiful no longer deconstructs the geometrical and Cartesian modeling of vision alone, but the entire metaphysical framework on which our world rests. Diderot remains vague, but already suggests that the foundations of religion are under attack. Yet here again, the blind man's incomprehension is turned on its head in the face-to-face encounter, and what he doesn't see ceases to be treated as lack, opening instead to a reappraisal of reality based on this emptiness, on this inaugural negation.

"How many principles for them that are nothing but absurdities for us, and vice versa." Through this reciprocity, which opens up the possibility of a chiasm, i.e. a vision, the blind man is no longer definitively the one who doesn't know or the one who knows less. The device reverses the lack, pivoting around the videntur: the blind man is seen not to know, and this subtraction given to see turns into the foundation of another, materialistic, atheistic knowledge. Yet the subtraction concerns precisely the Beautiful, this terrible absence for the blind man abandoned by Nature to his own defective nature, abandoned by the blind Beauty of the world to the sensitive monstrosity of his condition.

But it's not until the scene of Saunderson's last moments, and the merciless brutality of his deathbed dialogue with Pastor Holmes, that Diderot makes the content of this revolt explicit:

"The minister began by objecting to the wonders of nature: 'Eh! Monsieur, said the blind philosopher, leave there all this beautiful spectacle that was never made for me! I have been condemned to spend my life in darkness, and you quote prodigies to me which I do not hear, and which prove only for you and for those who see as you do. If you want me to believe in God, you must make me touch Him."" (P. 48.)

The condemnation to darkness is reminiscent of M. Hérault's cul de basse-fosse: Saunderson's revolt is indeed the same at the outset as that of the blind man in Le Puiseaux; it starts from the same stiffening in the subtraction of the Beautiful, in the lack of enjoyment. But the blind philosopher superimposes the resonance of the famous evangelical nisi immitam digitum: Saunderson's incredulity recovers the words of St. Thomas' incredulity. The Cartesian parallelism of vision and touch turns into an indictment of revelation.

III. From aesthetic monster to ideological monster

Internalization of the monstrous discourse

The reversal affects the device itself. The blind man's relationship with instituted discourse is reversed. When it came to vision, the instituted discourse was on the blind man's side: the accepted, Cartesian, geometric modeling of the visible, based on the identity of vision and touch, constitutes the blind man's world; the scopic irreducibility of vision, the Beautiful taken as a symptom of this irreducibility are phenomena external to the blind man, which the limit posed by his handicap points to as a supplement that is definitively foreign to him.

On the contrary, when it comes to revelation, the instituted, traditional and permitted discourse carried by Mr. Holmes becomes the discourse external to the blind man: the blind man's world is constituted by the disquieting strangeness of atheistic materialism. Here, God no longer appears as an incomprehensible supplement opening onto another world, but as an intellectual facility that discourages investigation and bridles knowledge:

"Is a phenomenon, in our opinion, above man, we immediately say, it is the work of a God; our vanity is not satisfied with less: could we not put into our discourses a little less pride and a little more philosophy? If nature offers us a knot that is difficult to untie, let us leave it for what it is, and let us not employ to cut it the hand of a Being who then becomes for us a new knot more indissoluble than the first." (P. 49.)

Of course, this discourse of Saunderson's is presented as a blind discourse in the same way as the Cartesian discourse on the visible; it is refuted by Diderot as soon as Saunderson is dead (pp. 52-53). But the reversal of the respective positions of the new discourse and the instituted discourse in the face-off between the blind man and the seer deconstructs this parallelism. The device of the Letter induces hors-discours a reversal. The Letter can only exhibit the blind man's truth; what remains here, around which it revolves, the irreducible datum of the real from which the constitutive reversal of the device operates, is this anti-profession of faith of the dying blind man, the horrible truth of this monstrous discourse. Saunderson depicts the reversing id in the image of the knot

.

As much as the discourse of Dioptrics distanced the blind man from reality, for which it substituted an abstract mathematical space, Saunderson's materialist discourse, on the contrary, brings the blind man back to the heart of reality, through the evocation of monsters. Monsters are the return effect, in the real, of the theological discourse on Beauty:

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"May I ask you, for example, who told you, Leibnitz, Clark and Neuton that in the first moments of animal formation, some were not headless and others footless? I can argue that these had no stomachs, and these no intestines; that such to whom a stomach, palate and teeth seemed to promise duration, ceased by some vice of the heart or lungs; that the monsters annihilated themselves successively; that all the vicious combinations of matter disappeared, and that there remained only those in which the mechanism implied no important contradiction and which could subsist by itself and perpetuate themselves." (P. 50.)

To the discourse on the wonders of nature, Saunderson thus responds with an evocation of monsters; to the rational principle of the orderly Creation of the world, he opposes a principle of chance and anarchy. The monster here becomes the norm for what nature produces; what in nature manifests a certain order, symmetry, beauty and stability in its organization constitutes, on the contrary, for Saunderson, the momentary exception. Through this reversal, this coup de force, the blind man takes his place in the world and legitimizes his monstrosity. He exhibits his sensitive monstrosity in the face of the blind, unreal beauty of this illusion of a theologically ordered world. The sensitive, brutal reality of the monster undoes the discourse of beauty.

The Molyneux problem, or the eye as device

After this brutal indictment of the Beautiful by Saunderson on his deathbed, it seems that nothing more of the jouissances proper to the visible can be saved. However, Diderot takes up the question in another way, with Molyneux's problem: the question is whether the blind child, coming to enjoy sight and seeing a cube and a sphere without being able to touch them, "will be able to discern them and tell which is the cube and which is the globe" (p. 56). But the essential problem for the blind is not to distinguish the cube from the sphere, but, more generally, to know whether the blind person will be able to see anything, and under what conditions, within what timeframe. Molyneux's problem turns out to be absurd and undecidable; Diderot highlights an assumption implicit in this debate, and he rejects it categorically: by asking whether the blind man who distinguishes the cube from the sphere by touch will, after his operation, distinguish the cube from the sphere by sight, Molyneux implicitly subordinates sight to touch; he makes sight another touch, a metaphorical touch, following in this the modelizations of Cartesian Dioptrics whose limits Diderot has marked. Molyneux's problem comes down to whether the blind person will spontaneously perform the metaphor of tact to sight, or whether he will have to re-appropriate this metaphor through the new experience of his hands conjoined with his eyes.

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Or the encounter with the "truly" blind, those in whom we don't take an interest only once they've become sighted, has brought out, as we've seen, this scopic irreducibility of what in vision returns and is not translated into touch. Diderot radicalizes and generalizes his position in this final part of the Lettre, showing that irreducibility is specific to each sense. The eye distinguishes forms by its own means, through color in particular, means that have nothing to do with the geometrical modeling of touch.

The eye is itself a device. It will be advisable to allow "all the time necessary for the eye's moods to dispose themselves properly" (p. 63). Once the cataract operation is complete, only this arrangement of the parts will make vision possible. Through the deconstruction of Molyneux's problem, Diderot's virtual blind man is thus seen to be unable to see, despite his operation. He sees mechanically, as the surgical lowering of the cataract restores the geometrical field of vision; but he does not see physiologically until the humours, the cornea, the sloe, the retina are accommodated to vision. Thus completes the reversal of the videntur and the hijacking of the Virgilian exergue: possunt nec posse videntur, they can see and we see that they cannot.

Beauty as surface

Diderot's description of this physiological specificity of the ocular device, where the eye no longer functions like the Cartesian mirror but in the continual movement of deformations, conformations, curvatures of its soft parts, unexpectedly brings us back to the evocation of beauty: "there is no painter skilled enough to approach the beauty and exactitude of the miniatures that are painted in the depths of our eyes" (p. 63). The beautiful miniature is the new beauty, in this semiology of the device that gradually takes possession of the text. This beauty projected onto the back of the eye no longer has anything to do with the theological wonder of a created world; it is the rigorous, photographic identity "of the representation to the represented object" (ibid.). It is a beauty no longer of admiration, but of rapport.

But above all, the new beauty, in the physiological device of the eye compared to a painter in miniatures, is a surface beauty. It is painted "in the depths of our eyes", it is the "canvas" of an inner "painting". Beauty has to do with an imaginary of surfaces.

This imaginary of surfaces that models beauty insofar as it is understood in the device of vision is an imaginary accessible to the blind. For the blind, it materially represents the limit in the face of the irreducible. For the blind man at Le Puiseaux, the surface of the mirror was the starting point of the enigma of the visible. As for Saunderson, he had demonstrated a kind of voir-peau, he had tried to make his whole body a sensitive surface making up for the absence, in him, of the organs of sight:

"Saounderson therefore saw by the skin; this envelope was therefore in him of such exquisite sensitivity, that we can assure that with a little habit, he would have managed to recognize one of his friends, whose portrait a draughtsman would have traced on his hand, and whom he would have pronounced on the succession of sensations excited by the pencil; it's Monsieur un tel. So there is also a painting for the blind; one to whom their own skin would serve as canvas." (P. 47.)

This paradoxical sensibility of the blind, whose skin becomes a support for the painting of the world and for whom aesthetic enjoyment materializes in a delicate shuddering of his entire bodily envelope, prepares the advent of a phantasmatic of surfaces, membranes, walls. The exquisite experience of seeing-skin in fact turns into the anguished representation of a skin walling up the man's body, obstructing his mouth. Saunderson hypothesizes this, when he evokes the monsters that nature is capable of producing:

"if the first man had had a closed larynx, had lacked suitable food, had sinned in the parts of generation, had not met his mate, or had spread into another species, Mr. Holmes, what would have become of the human race? it would have been enveloped in the general depuration of the universe" (p. 51).

The closed larynx makes it impossible to scream. The succession of monstrous hypotheses poses a series of phantasmatic equivalences: if the larynx is closed, the cry can't come out; from there we move on to food that can't go in, then to penetration that can't happen. Man is monstrously imagined as a pure surface. He then slips into universal defecation, i.e., into the reversion of impossible absorption or penetration. He does not slide, moreover; he is enveloped, a surface caught in another surface.

This imaginary of surfaces reappears in a completely different context, during an experiment imagined by Diderot:

"If one were to place between your thumb and forefinger, unbeknownst to you, a paper or some other plain, thin and flexible substance, it would be only your eye that could inform you that the contact of these fingers would not be made immediately. I would observe in passing that it would be infinitely more difficult to deceive a blind person on this point, than a person who is accustomed to seeing." (Pp. 62-63.)

Once again, with this experiment, Diderot proves that touch does not account for everything that is accessible by sight: the eye sees but the fingers do not feel the leaf placed between thumb and forefinger. Yet the experiment immediately backfires: the blind person, whose tactile sensitivity is more developed, will feel the leaf that the sighted person will not have noticed. Something thus turns around a surface, around this "plain, thin, flexible substance" that figures both the limit of the visible and the tactile and, each time, refers to their respective irreducible excesses.

Finally, in Molyneux's problem, Diderot surreptitiously substitutes the circle for the sphere, the square for the cube because, he says,

"he who uses his eyes for the first time sees only surfaces, and that he does not know what it is to protrude; the protrusion of a body to sight consisting in the fact that some of its points appear closer to us than the others" (p. 69).

This term saillie is strange, instead of the word relief, used several times in the Lettre. How can we not perceive in it the echo of a signifiance, of that other saillie which, according to Trévoux, "is also said when speaking of the mating of some animals". This active verb "is synonymous with cover, & is conjugated like saillir a hydraulic term". We're definitely in the middle of fluid physics: the physiological description of the ocular device and its moods led there. And hadn't Saunderson slipped from seeing-skin to closed larynx, then to some sin in the conformation of the "parts of generation"

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The surface as subversive jouissance

A phantasmatic continuity is thus sketched out between the beautiful surface that the world imprints in miniature on the back of the eye, and the surface that marks the boundary between the Cartesian modeling of the gaze and the non-modeling dimension of what, in the visible, is a matter of scopic irreducibility. The surface is both the support and the model of vision; it intervenes technically and symbolically in its phenomenological description. Through this double articulation, both structural and signifying, the surface constitutes a device from which Diderot will deploy an entire sexualized imaginary of the membrane, insofar as at once it corporizes, fetishizes the modelizations of the old world, logocentric and Cartesian, and, through this fetishization, surpasses and inverts these modelizations.

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The imaginary of the membrane has in this way to do both with the ideal, but reductive, formalization of the Beautiful and with its overcoming, its monstrous reversal, through which to think a symbolic refoundation. This functionality of the surfaces implemented in the Lettre sur les aveugles becomes clearer when this text is placed in relation to its novelistic corollary, Les Bijoux indiscrets.

The ritual of the returned magic ring, in Les Bijoux, supplements, in the very monotony of its repetition, what Mangogul would like but cannot know about his favorite: is she faithful and, behind this questioning, is she satisfied? The essays are thus, like the experiments in Lettre sur les aveugles, supplements to an inaugural experience that is lacking. They scrutinize the mystery of the female sex grasped in its ambivalence of sensitive surface and openness, or in other words of smooth, flat speaker, words without feints or ulterior motives, and of witness in relief, bearing a subversively critical gaze. Two gazes intersect: Mangogul's and that of the sex that speaks, at the edge, at the sensitive surface of sex that is open to speech for a moment. This crossing is the very gaze modeled by the Letter on the Blind.

Finding the beauty of the beloved woman presupposes this stopping short of the envelope, the membrane, this suspension of the gaze, this respect for the other sex. At the other end of Diderot's work, the Marquis des Arcis, in the story of Mme de la Pommeraie, has the same experience and faces the same face-to-face confrontation as the Mangogul in Bijoux.

At the beginning of Lettre sur les aveuglesthe one who evades the eye of the observer is the demoiselle Simoneau operated on by Réaumur, a Simoneau that Diderot will change into Suzanne Simonin, revolting against the veil that obstructs her in La Religieuse : the same veil-membrane where female jouissance is played out, right up to the homosexual hysteria of Sainte-Eutrope's superior.

The 1782 addition to the Lettre sur les aveugles restores in extremis, at the end of the text, the presence of the beautiful blind virgin, Mlle de Salignac, Sophie Volland's niece. The eyeless woman is then given to us to see, in her monstrous beauty.

It's not so much a question here of the other jouissance where the secret of a feminine knowledge would reside, but rather, faced with the geometrical protrusion, in the quivering of the membrane, of the deep spring of all subversive thought. It is always this moment that, in the last resort, is given to see as the theatrical moment of a poetic recapture:

"The patient was seated; now his cataract was removed, Daviel placed his hand over eyes he had just reopened to the light. An elderly woman, standing next to him, showed the keenest interest in the success of the operation; she trembled with every limb at the operator's every movement. He beckoned her to come closer and placed her on her knees opposite the patient; he moved his hands away, the patient opened his eyes, he saw, he exclaimed: Ah! it's my mother!..." (Pp. 97-98.)

From maternal trembling to blinded face-to-face, then to vision and cry, what is revealed in this scene of vision, in its irreducible beauty, is the reunion with the archaic bond, this powerful vision, beyond the beautiful and the monstrous, of the mother-surface that envelops, and which in Diderot founds materialist thought.

Notes