Diderot’s Letter on the Blind as Disability Political Theory

The Letter’s Context

The Letter is addressed to an unnamed “Madame” (possibly author Madeleine d’Arsant de Puisieux, Diderot’s lover) ³⁴ about a cataract removal for a blind young woman; the French ophthalmologist Jacques Daviel had created a new procedure involving surgical removal of the lens just two years prior, in some cases producing sight. ³⁵ “Madame’s” and Diderot’s attendance was denied because the doctor wanted only witnesses of “no consequence” (171), a claim that resulted in Diderot’s imprisonment, though apostasy in the Letter was another likely reason. ³⁶ So Diderot instead offers Madame his philosophical reflections on blindness and vision as a “substitute for the spectacle I so rashly promised you” (171).

What made attendance at this “spectacle” significant was the aforementioned question that William Molyneux posed to John Locke, discussed in his Essay Concerning Human Understanding. Locke agrees with Molyneux that “the Blind Man, at first sight, would not be able with certainty to say, which was the Globe, which the Cube, whilst he only saw them: though he could unerringly name them by his touch.” ³⁷ Knowledge acquired through touch would not be automatically transferred to another sense, as would be the case if ideas were innate as rationalists claimed. For “all Children and Ideots have not the least Apprehension or Thought” of such principles, which they would if rationalists were correct. Moreover, “To say a notion is imprinted on the mind, and yet at the same time to say, that the mind is ignorant of it, and never yet took notice of it”—which would presumably be the case for a blind person as much as the “Ideot”—“is to make this impression nothing.” ³⁸

For Locke, all the senses convey perceptions that are the foundation of ideas; and further, the senses are interdependent. Since “Figures”—like a cube and a sphere—are among the “Ideas we get by more than one Sense,” most particularly “the Eyes and Touch,” then “we bring ourselves by use, to judge of the one by the other.” ³⁹ But sight is “the most comprehensive of all our Senses, conveying to our Minds the Ideas of Light and Colours, which are peculiar only to that Sense; and also the far different Ideas of Space, Figure, and Motion.” ⁴⁰ Given that “Perception [is] the first step and degree toward Knowledge, and the inlet of all the Materials of it,” it follows that “the fewer Senses any Man . . . hath; and the fewer and duller the Impressions are, that are made by them; and the duller the Faculties are, that are employed about them, the more remote are they from that Knowledge, which is to be found in some Men.” ⁴¹ Blind persons lack the most important sense, and their touch is both inferior to sight and to sighted persons’ touch, since they cannot integrate it with sight. They thereby have inferior access to knowledge, just as an “Ideot’s” lack of reason limits his.

This is the primary ground on which Diderot challenges Locke, rejecting the primacy of vision and the necessity of sight to touch. He does so by mocking the hypothetical model that Molyneaux posed and the irresponsible use of cataract surgery. Since the operation that inspired the Letter was to be performed by the Prussian occulist Joseph Hillmer, many of whose patients, though able to see immediately after surgery, became “inoperably blind within a few days,” Diderot’s apology to “Madame” is couched in terms that imply the futility of experimental observation. ⁴² Diderot further mocks the notion of the “experiment” itself, pointing out that “People are trying to give sight to those born blind, but on closer examination, I think it would be found that philosophy has as much to gain by questioning a blind man of good sense. He would explain how things happen inside him which could be compared to the way they happen inside us, and this comparison might solve all the problems that make the theory of vision and of the senses so complicated and uncertain” (204). Accordingly, Diderot relates accounts of Saunderson, who held the Lucasian Chair of Mathematics at Cambridge University, a prestigious professorship held by Isaac Newton and Stephen Hawking ⁴³ ; the “blind man of Puiseaux” who, though never named, is believed to be a real person ⁴⁴ ; and a blacksmith whose eyesight was restored by Daviel through removal of cataracts but who found that seeing made his work more difficult and so often closed his eyes, much to Daviel’s annoyance. From these, and a later encounter with musician Mélanie de Salignac, “We are drawn to the conclusion that the eye is not so necessary nor so essential to our happiness as we are inclined to believe,” ⁴⁵ a direct challenge to what today would be called the “ableism” of Locke’s view.

Diderot says the blind man of Puiseaux “speaks so well and so accurately on so many things that are absolutely unknown to him, that conversing with him would undermine the inductive reasoning we all perform, though we have no idea why, which assumes that what goes on inside us is the same as what goes on inside others” (172). At first glance, the reference to “things . . . absolutely unknown” may seem to indicate the inferiority of blind persons’ knowledge. But as Kate E. Tunstall suggests, Diderot is rhetorically adopting the biased views of his sighted readers to demonstrate all the more dramatically the errors they are subject to. ⁴⁶ For this man has knowledge of these things by experiencing them differently than sighted persons; for instance, when asked if he would like to see, the blind man says that he would prefer to have very long arms because he could tell more about the moon by touching it. Diderot then reports that the man leads a “normal” life and is not only married with children but works for a living as a bonnet-maker—though in “Aveugle” d’Alembert identifies him as a chemist and musician, and Margo, Harman, and Smith call him a “winegrower.” ⁴⁷

Diderot’s longest discussion is of Saunderson, author of the well-regarded Elements of Algebra, who became totally blind before the age of two. ⁴⁸ While communicating the disadvantages of blindness, Saunderson considers differences from sighted people in his modes of perception as difference rather than disadvantage. As an accomplished mathematician—indeed, specializing in optics (194)—he presents himself, and is presented by Diderot, as an able human being who relies on different perceptual cues and different empirical encounters with the world around him. Detailing at length the various accomplishments of Saunderson, including a complicated “machine for algebraic calculations” and geometric shapes consisting of pins stuck in boards in checkerboard patterns (185–92), Diderot says that “the sense of touch, when trained, can become more delicate than sight” (195).

The rebuke that philosophers obsessed with Molyneux’s hypothetical should speak with blind persons—not to mention Diderot’s evident disgust with those like Hillmer who botched many cataract surgeries—implies a strong disapproval of negative attitudes toward blindness. But it also suggests a certain contempt for the kind of arid philosophy that Molyneux’s hypothetical offers. The details that Diderot provides of the lives of these blind persons offers a much stronger basis, Diderot asserts, for accurate science and sound philosophy.

Molyneux’s Problem

Michel Foucault called Molyneux’s problem “one of the two great mythical experiences upon which the philosophy of the eighteenth century wishes to base its beginning.” ⁴⁹ It was particularly the subject of philosophical debate over the fifty years between Locke’s Essay and Diderot’s Letter, addressed by Berkeley, Condillac, and Voltaire. This fascination, of course, was not with blindness per se, much less with disability, but with knowledge, particularly the debate between rationalism and empiricism. The puzzle seems to present a profound metaphysical and existential problem of translation across the senses: communicating or explaining vision to someone who has never seen. As Bryan Magee argues, sighted people are so dependent on vision that imagining a coming-to-the-world without vision is often overwhelming. ⁵⁰

On Locke’s view, knowledge of the difference between a cube and sphere that is acquired by sighted persons entails a variety of sensory perceptions, and their interaction forms the data that makes up knowledge—which blind persons lack. Support for Locke’s response to Molyneux began with William Cheselden’s report on his 1727 operation to correct blindness in a young man who could not remember visually the difference between his dog and his cat, though could do so after touching the animals. ⁵¹ This sort of unscientific confirmation continues up through Oliver Sacks’s account of a man whose vision was corrected after forty years. ⁵² But the first controlled experiment to directly test Molyneux’s problem was not conducted until 2003 at Shroff Charity Eye Hospital in New Delhi, India. Five children aged eight to seventeen years old who were completely blind from infancy—four from cataracts, one from a corneal disorder—and whose vision could be completely restored underwent operations. The study put twenty different sorts of blocks on a table that could be seen and not touched; the children were given the same sorts of blocks to feel under the table, where they could not be seen. The experimenters “found a lack of immediate transfer”—that is, the children could not match the felt items with their correct seen counterparts. ⁵³ This suggested that Locke and Molyneux were correct.

However, the study found that “such cross-modal mappings developed rapidly,” ⁵⁴ suggesting that the “problem” with Molyneux’s problem was the requirement that recognition be instantaneous. This objection was anticipated by Diderot. As he argues, philosophers have “supposed that the man-born-blind would see as soon as his eyes were cured, and they have imagined that an eye that has had a cataract removed is like an arm that has recovered from paralysis. They claim that just as the latter does not need to exercise in order to have some feeling, so the eye does not either” (206). While sensation may return immediately to the arm, however, the muscles would be enervated and must gather strength, just as the signals between eye and brain that sighted persons have developed since birth would need time to operate fully. It would take time “for the eye’s humours to settle properly, for the cornea to acquire the necessary convex shape, for the pupil to be able to dilate and contract as it should, for the retina’s filaments to be neither too sensitive nor too insensitive to the effect of the light . . . for the optic nerves to become accustomed to transmitting sensation” (212). Moreover, the surgery itself was quite traumatic, cutting around the entire lens—with blades less refined than those available today—immobilizing the patient’s head with sandbags while it healed. ⁵⁵ This trauma to the eye is never recognized by Locke, Cheselden, or others; it is, Diderot notes, “a painful operation on a very sensitive organ that is disturbed by the slightest accident and often deceives those in whom it is healthy” (204).

He concludes “we must therefore agree that . . . we cannot see anything the first time we open our eyes; that in the first moments of vision, we can only see a multitude of blurred sensations that only become clear over time and as a result of our habitually reflecting on what is happening inside us” (210). The inability to recognize cube and sphere immediately does not prove that the subject, given time, could not fully understand what he was seeing even if he had not been permitted to touch the items in the meantime; “I should simply conclude that the organ needs experience, and not that it needs touch for that experience,” contra Locke (213). After all, “in order to be sure of the existence and shape of the objects we touch, we do not need to be able to see them. Why then would we need to touch objects in order to be sure we could see them?” (211).

The superiority and independence of touch is repeated in the Dream, where Diderot says all of the senses are “a kind of touch,” one involving the ear, the eyes, the palate, the nose; and the nerves that yield tactile sensation “form as many different kinds of touch as there are different organs and parts of the body.” It is this variability of touch, its “infinite variety,” that makes it an independent sense: if Mlle. de l’Epinasse injures her finger, she does not need to look to find the source of pain, she can feel it in her finger. ⁵⁶ But in the Letter, Diderot also challenges the assumption that “what the sense of touch would have taught a man-born-blind” is the same as what sighted philosophers themselves think they have learned through touch, noting that de Salignac could, by touch, “discern minute details in shapes and objects which often pass unnoticed by those who have the best of eyesight,” as he previously noted of Saunderson. ⁵⁷ Although touch and sight are each means of obtaining similar knowledge, simply assuming that the blind person makes the same tactile observations as the sighted person is mistaken. Locke, for instance, assumes that persons with all five senses have full and equal use of all. But Diderot believes blind persons have superior awareness of touch—through practice, and not being distracted by sight—so their tactile perceptions are superior, which could affect the outcome of the test.

Thus, part of Diderot’s critique is how unscientific empiricist partisans were in their approach to the puzzle. For instance, substituting a circle and square for the sphere and cube might produce different results, “because it very much appears that we can only judge distance by experience, and as a result, someone using his eyes for the first time will only see surfaces and not understand projection” (217). Similarly, presenting “a black cube and a red sphere on a large white background” would make it easier “to see the edges of the shapes” (212). All of these missing variables demonstrate that the “test” does not disprove rationalism, even if Diderot does not advocate it. But they also make the test virtually impossible to “pass”; the composition of Molyneux’s test ensures that subjects will fail, for complex visual images will take considerably more time for a newly sighted person to learn. For instance, articles of clothing “are laden with so many modifications, and their overall shape bears so little relationship to the parts of the body they are designed to adorn or cover, that Saunderson would have found it a hundred times more difficult to work out what his square bonnet was for than it would be for Monsieur d’Alembert . . . to work out what his tables were for” (217).

Diderot’s return to Saunderson at this point in the text suggests that Molyneux’s problem may also be inadequate in another specific way. In the “Addition to the Previous Letter,” Diderot reports that de Salignac, who had been trained in geometry, says that she can imagine a cube and a point in the center of the cube, and from there imagine the cube as four pyramids meeting in the center. ⁵⁸ He concludes from this that if her vision were corrected she would have an easier time recognizing the cube by sight than “a man with no education and no knowledge” (204). Diderot suggests that “a metaphysician familiar with the principles of physics, the elements of mathematics and the physical organization of the body” would be a more appropriate subject than the persons who had previously been drawn upon as “proofs” of Locke’s answer to Molyneux’s problem (204). Not only must the subject be highly educated, however; the conditions of a successful “test” would also require that only “the most talented of men and the finest of minds” be allowed in the “training and questioning a man-born-blind . . . a task not unfit for the combined talents of Newton, Descartes, Locke, and Leibniz” (205).

This apparent elitism on Diderot’s part seems to counteract the inclusiveness that underlies listening to previously excluded blind persons: must “blind men of good sense” also be highly educated? Adams observes that Diderot vacillated between “contempt for the ignorant, unlettered section of the population” and sympathy “towards the great mass of citizens, regarding them as downtrodden and repressed by tyranny.” ⁵⁹ Sympathy does not necessarily entail respect, but in the context of Molyneux’s problem, Diderot is suggesting that the hypothetical is what requires a mathematician’s skill, and examiners who are extraordinary intellectuals. That is (part of) what is wrong with it. His irony and sarcasm, so familiar to readers of Rameau’s Nephew, here aids in his muted mockery of Molyneux’s problem. But the larger point of the Letter remains: that “questioning a blind man of good sense”—including the bonnet-maker, blacksmith, and other persons of no great achievement—is more useful than contrived hypotheticals that depend on biased perspectives.

Blind Perspective

Thus, a central point of Diderot’s criticism is to correct sighted understandings of blind experience and the power relations that adhere to biased accounts of blindness. This aspect of his essay anticipates contemporary arguments that disability is not the tragedy that most nondisabled people believe it to be but rather entails a different way of relating to and perceiving the world that has value and worth. ⁶⁰ Yet an epistemological puzzle remains: When blind and sighted persons perceive things in different ways, does that amount to different knowledge altogether? Do blind and sighted know the same things differently, or do they know different things? And if they know different things, how can these be shared with others who lack the sensory ability to know them? Diderot answers that when de Salignac “discern[s] minute details” that sighted persons miss, she acquires data they lack, just as they know color, which she cannot perceive. So each reaches a different conclusion about the object in question, and one could argue that they thereby know different things. But they also could be said to know different parts of the same thing, and both parts taken together are necessary to “knowing” the object in question.

This is where “questioning a blind man of good sense” takes on a deeper signification, for blindness highlights the importance of language in the creation of knowledge across sensory differences. Diderot more fully develops this theme in Letter on the Deaf, but language plays an important if subtle role in his consideration of blindness. In Diderot’s narrative, blind persons hear the same descriptions and conversations about objects and other entities as sighted persons do, even if each does not have the exact same material referents to the words—for instance, touching a cube rather than seeing it. Diderot makes this point when he considers the blind man’s understanding of a mirror as “‘a machine . . . that projects things in three dimensions at a distance from themselves if they are correctly placed in front of it.’” Diderot comments:

Our blind man knows objects only through touch. He knows on the basis of what other men have told him that it is by means of sight that we know objects just as they are known to him through touch. . . . He also knows that we cannot see our own faces, though we can touch them. . . . Sight, so he is bound to conclude, is a kind of touch that only applies to objects other than our faces and which are located at a distance from us. Moreover, touch only gives him the idea of three dimensions and so he will further believe that a mirror is a machine that projects us in three dimensions at a distance from ourselves. (173)

Diderot urges us to “consider . . . the subtlety with which he had to combine certain ideas in order to arrive at” this definition (173), which he then lays out for the sighted reader so that it is understood as thoughtful and sophisticated rather than humorous or silly. Indeed, he subtly mocks rationalism by declaring that, “Had Descartes been born blind, he would, it seems to me, have congratulated himself on such a definition” (173). ⁶¹ Further, Diderot raises a metaphysical question: if Molyneux’s problem asks how to explain sight to those who have never had it, the blind man of Puiseaux suggests how to explain touch to sighted persons who think they know but do not. He then analyzes the process by which the blind man translates his own sensory perceptions into knowledge through the relation of abstract ideas. So language is key to understanding how knowledge works; though Diderot stresses that the blind man knows “only through touch,” he also acknowledges that he knows “on the basis of what other men have told him” (173), and he in turn communicates his own ideas derived from his perceptions. So rational deduction, induction, abstraction, and language are all combined with sensory perception to produce knowledge.

This scene illustrates the central tension in Diderot’s argument between knowing the same things through different means—sight versus touch—and knowing different things, but language is the bridge that crosses this divide. For even if touch and sight cannot yield the exact same conclusions, sighted persons can understand and appreciate the description the blind man offers. As Wittgenstein argues, we know things, and about things, by their being situated in a common language that enables us to talk about them with others and be understood. Diderot makes a similar argument through Saunderson. If sighted persons were to see a square and a circle that Saunderson could touch, what he felt “would allow me to arrange threads and position large-headed pins [on boards] in such a way” as to form the two shapes. How do we know that what he felt is what the sighted persons saw? Because “Those people who witnessed my demonstration of the properties of the circle and the square did not have their hands on my abacus, and they couldn’t touch the threads I had tied to make the outlines of my shapes; yet they could understand me. Therefore, they were not seeing a square when I was feeling a circle, otherwise we would never have understood each other” (216, emphasis added). Language bridges the distance between sighted and blind in sharing knowledge.

Language thus addresses Diderot’s “Montaigne-like pyrrhonism,” which poses the challenge: how can we know that any of our empirical perceptions are the same as others’? ⁶² Again, Wittgenstein is instructive; his “beetle in the box” confronts the inability to feel others’ sensations—perhaps coincidentally, Wittgenstein specifies pain, a sensation that can sometimes cause disability ⁶³ —by drawing a direct connection between tactile sensation and sight. In this “language game,” everyone has a box with something called a beetle in it. We cannot look into other people’s boxes, only our own. We thus have no idea whether what others see in their boxes is what we see—it might be a different object; it might even be empty, he says. ⁶⁴ So vision is already part of the “game,” as a means to communicate the nontransferability of physical sensation.

The irony of using a visual metaphor for tactile sensation might seem to exclude blind persons, but in fact it echoes Diderot’s puzzle. For Wittgenstein complicates the empiricist assumption that what sighted persons see is exactly what other sighted persons see. On the view posited by Locke and Molyneux, blind persons lack a sense that sighted persons have, and thereby receive less complete sensory perception, and less knowledge, than sighted persons; sighted persons can look into blind persons’ boxes but not vice versa. On Diderot’s reformulation, by contrast, each of them has a different set of perceptions, and neither can experience what the other experiences; neither can look into the other’s “box” just as Wittgenstein posits. Yet the two cannot be that different, or we could not communicate with one another through language about our beetles. Hence, Wittgenstein says that what is actually in the box is not important if we “suppose the word ‘beetle’ has a use in these people’s language,” in which case “the thing-in-the-box has no place in the language game at all.” ⁶⁵

Certainly, language has its limit in Diderot’s materialism; it is not the rules of language that define objects, but the materiality of the objects that sets the boundaries to language. In this sense, he and Wittgenstein diverge. If Wittgenstein believes that what is in the box is “not a something” but “not a nothing either” because we can understand each other as we talk about our respective beetles as if they were the same thing ⁶⁶ , for the materialist Diderot what the blind person perceives by touch is in fact a something and cannot be that different from what the sighted person sees. That is why they can understand each other: materiality sets parameters to what we can perceive, regardless of which senses we use.

Yet Diderot does not follow Locke, either, who believed that language simply mirrored physical objects in the world. As Jay notes, Diderot maintained that “an epistemology based solely on the model of instantaneous vision was inadequate because it failed to register the inevitably temporal dimension of its linguistic mediation”; language mediates between our perceptions of the physical world and our understanding of those perceptions. Yet he also “acknowledged an inevitable disparity between our sensual experience and its linguistic mediation,” ⁶⁷ for whereas the physical world is given as it exists outside us, language is something that is socially produced and created. That “disparity,” which I am suggesting is uncovered by considering the experiences of blind persons, creates a shift in how Diderot thinks about empiricism; for his materialism acknowledges that there are material properties that we cannot yet perceive, such as the soul, a theme he pursues in D’Alembert’s Dream, where Diderot confronts the vastness of what science does not yet know and still needs to discover. ⁶⁸ Blind persons’ touch, Diderot suggests, similarly provides evidence of objects that sighted persons cannot, or do not, perceive, and hence talking to them will enhance their learning and knowledge of those objects.

This does not create a new epistemology; Diderot is still dedicated to empiricism. But, as in the Dream, he expands our limited assumptions about what empirical observation entails. When the Letter refers to the importance of touch to the blind person’s ability to perceive the material world, it is important that touch is the tool through which she can translate that world into concepts so that she can participate in language and social relations in the world around her; it is not the limit of her knowledge, any more than vision produces direct and unmediated access to knowledge. Sight provides only partial information, and attending to perceptions of blind persons will provide different but related information to help approximate more complete knowledge. That is why sighted persons must question blind persons: communication of knowledge between persons is an important part of the equation for understanding. Even if some things may be primarily apprehended by sight, like a reflection in a mirror, such primacy does not necessarily entail exclusivity.

This theme of language may seem to have taken us away from disability. But Diderot is suggesting that different sensory experiences are valuable in the accumulation of knowledge, and language is the means of sharing them and thereby also of constituting knowledge. Although Diderot’s skepticism suggests that we can never be entirely sure that what others perceive is the same as what we perceive, the fact that we can communicate successfully about them is relevant to our shared knowledge of those things. Certain statements about the cube and the globe—like the beetle—will make sense, leading us to form judgments and make knowledge claims. Other statements may appear not to make sense, and we will not know what to make of them, as Saunderson suggests. But it is the struggle to make sense that will determine whether they enter into language and thereby into knowledge. ⁶⁹ Insofar as blind persons rely on different sensory perceptions than sighted, they take these as the foundation for their participation in the language games of those around them, usually sighted persons.

In some games they are more successful than in others, however, because the rules are determined by and for sighted experience; such relations of power can prevent the sighted from hearing what blind persons say. Diderot shows that sighted persons’ assumptions about blind experience and knowledge are wrong, that blind people’s abilities produce valuable knowledge. Tunstall points to the Letter’s epigraph, “Possunt, nec posse videntur,” which modifies a line from Virgil, “Possunt, quia posse videntur,” which means “They can, because they think they can,” (suggesting “the power of positive thinking”) or “They can, because they are seen to be able to” (which “makes a claim for causal links between seeing seeming and power”). But, she notes, Diderot “replaces Virgil’s ‘quia’ with an opposition, ‘nec’: They can though they don’t look as though they can.” ⁷⁰ As the blind man of Puiseaux says in exasperation, “‘It is clear to me, Gentlemen, that you are not blind, since you are surprised at what I can do. So why aren’t you also amazed that I can speak?’” (178). According to Diderot, he can speak eloquently and profoundly; he knows many things of which sighted people assume he cannot, and they could benefit from listening to him.

The Letter as Disability Political Theory

Diderot thus engages a political argument about the ways knowledge is gathered, evaluated, and interpreted through relationships of power. By taking blindness as a condition of possibility rather than limitation, Diderot challenges the power that adheres to ableist views of impairments. More specifically, he critiques the idea that blindness is a medical condition that must be “cured” (known in contemporary disability studies as the “medical model”) and instead identifies it as an impairment that is turned into a disability by prejudicial attitudes and assumptions about blind persons’ abilities. He thus can be read as an early forerunner of what is called the “social model” at a time when the medical model was starting to burgeon in response to Enlightenment advances in medicine, such as cataract surgery, which changed disability from a condition of God’s will to something that humans could “treat” and control. Yet at the same time, he also anticipates more recent critiques of the social model that it reduces the body to a social construct; in recognizing the “trauma to the eye” produced by cataract surgery, Diderot recognizes that the materiality of the body is important to understanding blindness and blind experience. ⁷¹

From a political theory perspective as well, Diderot politicizes the body and its relation to knowledge. This politics may not be obvious, for Diderot’s materialist determinism might seem to suggest that blind and sighted people cannot help the fact that they know differently—it is determined by their bodies. This materialist determinism unavoidably carries a negative moral valence that has haunted disability throughout history and runs against contemporary disability studies’ stress on disability’s fluidity. ⁷²

But believing in natural liberty at the same time, as well as natural sociability and the primacy of reason to human nature, Diderot’s argument, as I have demonstrated, also shows that how we acquire knowledge, and what we do with it, is a function of power. ⁷³ Diderot notes that the relationship between “sensations” and “what occasions them” is “purely conventional,” learned by “experience alone” (210); so how we read the bodies of knowers is something that we can choose to direct to more inclusive approaches. The reading I have given suggests that Diderot is arguing for a reinterpretation of blind bodies and the kinds of knowledge that their materiality produces, such as heightened awareness of touch, that has implications for the distribution of power and the relation between power and knowledge.

Political theory’s attunement to the politicization of bodies and the power/knowledge nexus can make significant contributions to disability and would benefit from joining this conversation. Despite being a relatively interdisciplinary subfield within political science, political theory lags behind other fields in considering disability as an important topic of study. History, anthropology, sociology, English, and even our cousins in philosophy have all paid considerable attention to disability while our own field continues to ignore it, much as we lagged behind these other fields in considerations of gender thirty years ago. ⁷⁴ Including disability experience in examining central categories of theoretical exploration can produce more thorough analyses.

Diderot shows us that specific impairments like blindness open up different ways of thinking about power, knowledge, inclusion, and voice, all of which are significant topics for political theory. His critique of doctors trying to “cure” blindness and the philosophers seeking to use such procedures to test a hypothetical puzzle reveals the power relations in silencing the perspectives of blind persons. Though Saunderson was a famous professor, and the blind man of Puiseaux and Mélanie de Salignac had sufficient wealth to protect them, many blind persons at this time, including many of those subjected to the traumatic cataract surgery, were poor and illiterate. ⁷⁵ Political theorists’ attention to excluded groups, such as the poor, racial minorities, women, and sexual minorities, provides a promising foundation on which to explore how power produces and reproduces disability as well. Just as Diderot’s attention to blindness shows us the biased power moves in epistemological theory, so can attention to cognitive disabilities reveal important insights about democratic deliberation, or attention to mobility impairments challenge the ways in which we define freedom and restraint. ⁷⁶ Other categories of political thought could be deepened by attention to a wide range of disabilities.

The epistemic injustice produced by our ignoring such experiences and persons results in a political theory that is distorted by relations of power. Diderot offers a political critique of the social relations surrounding theoretical reflection; in particular, negative assumptions about blind persons’ knowledge and their resulting exclusion from intellectual discourse means that the empirical evidence that blind persons could contribute is lost. His critique of philosophers favoring hypothetical blind persons to real ones suggests that the knowledge and experience of blind persons can make valuable contributions to collective understandings of the world. Admittedly, his argument is couched less in terms of injustice than bad science and bad philosophy; assuming what blind persons can and cannot do and know, and arranging elaborate and flawed “experiments,” rather than simply speaking with them, is epistemically foolish. That Diderot himself does not claim it is also unjust, however, does not prevent contemporary theorists from characterizing it as such, and from using Diderot’s argument to make a political and ethical case for the inclusion of disability perspectives. Political theoretical work on the systematic exclusion of minority groups suggested earlier could benefit from Diderot’s “scientific” arguments by changing the angle from which we read disabilities like blindness.

For instance, framing blind persons’ knowledge in terms of the power of sighted persons to define dominant norms suggests that, instead of deducing moral inferiority of blind persons from their inability to see nakedness, perhaps the fault is with the sighted, who suffer from an exaggerated fear or shame of bodies. Indeed, in Supplément au Voyage de Bougainville, Diderot offers a parallel critique of dominant western assumptions of moral superiority over Tahitian natives, suggesting that the corrupt “particular” morality of European society puts it in no position to judge Tahitians (who, echoing the Letter, were unashamed of nakedness). ⁷⁷ Though as Stanley notes, the essay “undermines any clear opposition between virtuous nature, represented by Tahiti, and corrupt civilization, represented by Europe” (such as Tahitians’ apparent celebration of sex as “natural” masking a sexist treatment of women as solely valued for their reproductive abilities), ⁷⁸ Diderot suggests that Europeans damaged Tahitian society by introducing syphilis, violence, and norms of proprietariness. ⁷⁹ But more important than pointing out European hypocrisy is that Diderot seeks to reconstruct the story from the perspective of the Tahitians, just as he tries to communicate reality from the perspective of blind persons. From this nondominant perspective, he can demonstrate that the Tahitians are in some ways superior even as they have their own moral flaws and ambiguities. By analogy, Diderot is suggesting that blind persons are not just “equal but different” when compared to sighted persons, but also in some ways superior in their attentiveness to the senses, which is the basis for empirical observation, and their eagerness to acquire new knowledge. Blind “culture,” so to speak, like Tahitian culture, is undervalued by dominant perspectives but has much to teach scientists and philosophers. Similarly, if the soul is located in the fingertips as he suggested in the Dream, Diderot’s discussion of Saunderson’s deathbed conversation takes on new significance, for perhaps Saunderson is correct in his atheism; perhaps blindness gives him superior moral knowledge. Such a conclusion would cohere with the belief that Diderot endorsed atheism, a contributing reason for his imprisonment.

The Letter also offers methodological contributions to political theory in its subtle but effective critique of hypotheticals. Using hypotheticals, Diderot shows, produces errors in philosophical reasoning by reinforcing existing biases—in this case, over-reliance on and over-valuing of sight, suggesting that empiricism must rely on a greater variety of inputs than it has heretofore assumed. This offers a particular configuration of the power/knowledge nexus in the power of sighted philosophers and scientists alike to privilege a particular source of knowledge and to ignore the knowledge blind persons offer. Urging a methodological shift from “pure” abstract reason to the use of narrative in acquiring information as the foundation for theory, Diderot’s advocacy of blind persons’ accounts of their own experiences suggests a disability politics of self-representation; sighted persons should hear what blind persons say in their own words and not impose their own interpretation on blind experience. Diderot’s remarkably forward-looking argument about blind persons indicates that their lives contain richness and complexity of experience that has not been imagined possible by sighted persons and demonstrates that how they experience their own lives is not how sighted persons imagine them. By analogy, other sorts of evidence should be available through consideration of other kinds of impairments. Not only would this enhance the kinds of knowledge we can develop about our social and political world, it would contribute to political theory’s ongoing project of making the development of knowledge more inclusive.

I have suggested that Diderot’s presentation of blindness is political because he identifies power operating in the reading of blind bodies and experience by the sighted and how blind persons negotiate and resist such readings. In particular, Diderot’s attempt to make his readers “see” blind people as full human beings who can accomplish many things assumed impossible suggests a political defense of the value of sensory difference that recognizes the power inherent in the language used to describe blind persons as “creature[s] whose significance was strictly limited to the interpretation of a pathological problem and to the correction of [their] anomaly.” ⁸⁰ Molyneux’s problem is a keen example of this and is designed to get the answer it wants by putting the burden of unrealistic expectations on blind persons, expectations that arise out of ignorance of blind persons’ experience and of the human body. Instead, Diderot’s Letter suggests that accurately evaluating blind persons’ abilities will enhance the accuracy of knowledge, revealing a significantly different, and more accurate, understanding of the world around us. Attending to disability, both as it is represented in canonical theory and as a contemporary subject to which we bring our texts to bear, is an important frontier for the field of political theory. Diderot’s Letter provides a valuable contribution to such a project.