On 7 July 1688 the Irish scientist and politician William Molyneux(1656–1698) sent a letter to John Locke in which he put forwarda problem which was to awaken great interest among philosophers andother scientists throughout the Enlightenment and up until the presentday. In brief, the question Molyneux asked was whether a man who hasbeen born blind and who has learnt to distinguish and name a globe anda cube by touch, would be able to distinguish and name these objectssimply by sight, once he had been enabled to see.

• 1. Molyneux’s Formulation of the Problem
• 2. Eighteenth-Century Philosophical Discussions about Molyneux’s Problem
• 3. The First Experimental Data
• 4. Empirical Approaches in the Nineteenth Century
• 5. Modern Approaches
• 6. Conclusion
• Bibliography
• Academic Tools
• Other Internet Resources
• Related Entries

1. Molyneux’s Formulation of the Problem

As is apparent from both his writings and his lectures, Molyneux washighly interested in optics and in the psychology of sight. To someextent this simply reflects the general attitude of his time: opticswas a subject that was then engaging the attention of a number ofleading scientists. His interest also had a more personal background,however, for his wife had lost her sight in the first year of theirmarriage. The immediate cause of his formulating the problem andsending it to Locke is to be found in Locke’s French extract ofAn Essay Concerning Humane Understanding, published in 1688in theBibliothèque Universelle & Historique. Inthis extract Locke distinguished between ideas we acquire by means ofone sense and those we acquire by means of more than one sense. Hemaintained that someone who lacks a sense will never be able toacquire the ideas pertaining to it. A blind man, for example, willnever be able to have any idea of colour. Among the ideas we are ableto acquire by means of a combination of senses, Locke reckoned thoseof space, rest, motion and figure. Molyneux’s problem had to dowith the last of these. Molyneux was probably inspired byLocke’s exposition of the ideas of persons born blind and theideas which can be acquired by means of both sight and touch. He was,moreover, a great admirer of Locke. (Although earlier we suggestedthat Molyneux might have been inspired by Ibn Tufail’stwelfth-century philosophical novelHayy ibn Yaqdhan, whichhad just been published in Latin (1671) and English (1674) and alsohad an influence on Locke, there seems to be no indication thatMolyneux read Ibn Tufail.)^[1]

On Saturday 7 July 1688 William Molyneux wrote a letter to John Lockesetting out for the first time his problem concerning the person bornblind:

Dublin July. 7. 88

A Problem Proposed to the Author of the Essai Philosophiqueconcernant L’Entendement

A Man, being born blind, and having a Globe and a Cube, nigh of thesame bignes, Committed into his Hands, and being taught or Told, whichis Called the Globe, and which the Cube, so as easily to distinguishthem by his Touch or Feeling; Then both being taken from Him, and Laidon a Table, Let us Suppose his Sight Restored to Him; Whether heCould, by his Sight, and before he touch them, know which is the Globeand which the Cube? Or Whether he Could know by his Sight, before hestretch’d out his Hand, whether he Could not Reach them, thothey were Removed 20 or 1000 feet from Him?

If the Learned and Ingenious Author of the Forementiond Treatise thinkthis Problem Worth his Consideration and Answer, He may at any timeDirect it to One that Much Esteems him, and is,

His Humble Servant
William Molyneux
High Ormonds Gate in Dublin. Ireland

For reasons unknown Locke never replied to the letter. However, acouple of years later, after the two men had started an amicablecorrespondence, Molyneux returned to his problem. This time withsuccess. In his letter, dated 2 March 1693, Molyneux presented Lockewith his problem, though in a somewhat altered form, asking Locke ifhe could perhaps find some place in hisEssay to saysomething about it. This time Locke reacted with enthusiasm:“Your ingenious problem will deserve to be published to theworld.” From the second edition of hisEssay (that of1694) Locke included Molyneux’s problem in his work and therebymade it accessible to a wider audience:

Suppose a Man born blind, and now adult, and taught by his touch todistinguish between a Cube, and a Sphere of the same metal, and nighlyof the same bigness, so as to tell, when he felt one andt’other; which is the Cube, which the Sphere. Suppose then theCube and Sphere placed on a Table, and the Blind Man to be made tosee. Quaere, Whether by his sight, before he touch’d them, hecould now distinguish, and tell, which is the Globe, which the Cube.

In this formulation Molyneux’s problem attracted the attentionof lots of philosophers and other men of learning, such as Berkeley,Leibniz, Voltaire, Diderot, La Mettrie, Helmholtz and WilliamJames. In which ways did they approach the problem?

2. Eighteenth-Century Philosophical Discussions about Molyneux’s Problem

In the first instance, philosophers considered it to be impossiblethat a man born blind should be able to acquire sight. They regardedMolyneux’s problem as a kind of thought-experiment, which was tobe dealt with by ratiocination alone. The arguments put forward wereusually concerned with the relation between visual and tactualsensations or between visual and tactual notions of the form ofobjects.

All these philosophers assumed that the visual and tactual sensationsof an object differ from each other, but there was no agreementconcerning the relation between the two. Some, Berkeley for instance,believed that this relation is arbitrary and based only on experience.Others, such as Lee and Synge, thought that it is necessary andperceived directly, while yet others, such as Molyneux and Locke,thought that it is necessary and learned by experience. Opinions werealso divided concerning the relation between visual and tactualnotions of objects. Some philosophers defended the position that thevisual and tactual notions of a globe differ from one another, and canonly be related by either experience or reason (the latter view wasdefended by Reid). Others believed that the visual and the tactualnotion of a globe are actually the same, or have something in commonwhich is either observed directly (Boullier and Hutcheson) or inferredby reason (Leibniz).

Investigating how the different positions correlate with the answersgiven to Molyneux’s question, one can conclude as follows.Empiricists such as Molyneux, Locke and Berkeley answered in thenegative. More rationalist philosophers such as Synge, Lee and Leibnizgave an affirmative answer. There was no unanimous solution, amongstothers because Molyneux’s problem was interpreted in differentways. Some philosophers thought that the man born blind had to answerdirectly, while others were of the opinion that he should be able tomake use of his memory and reason, and that he should be at liberty toview all sides of the objects by walking around them. Somephilosophers believed that the question implied that the man should betold in advance that he would be presented with a globe and cube,whereas others thought that he should not be provided with thisinformation.

3. The First Experimental Data

Discussion concerning Molyneux’s problem took a new turn oncethe English surgeon and anatomist William Cheselden (1688–1752)published an account of what a congenitally blind person had seenafter his cataracts had been removed (1728). The publication ledphilosophers to regard the Molyneux problem no longer as a simplethought-experiment, but as a question which could be answered byexperimentation.

In his account, Cheselden noted that when the boy—who recentlyhas been identified as Daniel Dolins—was first able to see, hedid not know the shape of a thing and could not recognize one thingfrom another, regardless of how different in shape or magnitude they were.^[2] Some philosophers thought that Cheselden’s observations wereunequivocal and that they confirmed the hypothesis that a blind manrestored to sight would not be able to distinguish objects and wouldhave to learn to see. Most of these philosophers, we might mentionVoltaire, Camper and the elder Condillac as examples, were adherentsof Berkeley’s theory of vision, which had predicted a similaroutcome.

Others, however, such as La Mettrie and Diderot, regardedCheselden’s account as wholly ambiguous in its implications.They pointed out that it was possible that the boy had been unable tomake valid perceptual judgments because his eyes had not beenfunctioning properly. They suggested that this could have been due tothe fact that his eyes had not been used for a long time, or to theirnot having had enough time to recover from the operation. They pointedout that Cheselden had, perhaps, asked the boy leading questions. Somephilosophers also believed that the results of the inquiry depended onthe intelligence of the patient.

Those who criticised the significance of Cheselden’s account inthis way (most of them were Frenchphilosophes) madeproposals as to how to avoid the problems mentioned. They suggestedthat one should prepare the patient carefully for the operation andfor the interrogation, that one should allow his eyes time to recoverfrom the operation and that one should give him the opportunity toexercise his eyes in darkness. What is more, one should avoid askingleading questions.

Some philosophers were even more radically critical of operations likethat performed by Cheselden. Mérian, for example, noticed thatCheselden’s observations, like all observations of blind peoplewhose cataracts have been extracted, present difficulties becausecataracts do not cause complete blindness and complete blindnesscannot be cured. It could not be concluded from this thatMolyneux’s problem could not be solved experimentally, however,for it could be maintained that patients operated upon for cataractsare directly relevant to the solution of it. They are unable toperceive form before they are operated upon, and the essential issueat stake when posing Molyneux’s problem is the ability todistinguish and name forms. This is a point of view which was taken bymany philosophers.

4. Empirical Approaches in the Nineteenth Century

About 1800 several developments occurred which justify the speaking ofa new period in the history of Molyneux’s problem. New accountsof patients operated on for cataracts were published, and shed freshlight on the issue. Whereas Cheselden had only noticed what hispatient observed in more or less natural circumstances, laterophthalmologists performed experiments which showed whether theirpatients were able to see form, size, distance, etc. Some, such asFranz and Nunneley, were especially interested in Molyneux’sproblem as such, and performed experiments with the prescribed globeand cube. Some of the reports were in agreement with that ofCheselden, others conflicted with it. The cases could not easily becompared, however, since the pre- and post-operative circumstancesdiffered to such a great extent. As one might have expected, anextended scale of possible solutions to the Molyneux problem wasbrought under consideration.

What is more, specialists also began to consider observationsconcerning the sight of newly born animals and babies when discussingMolyneux’s problem. Some of those doing research in the field,such as Adam Smith and Johannes Müller, supposed that the sightof young animals could be compared with that of a person who had beenmade to see. The fact that certain animals see objects at a distanceas soon as they are born suggested that Molyneux’s questioncould be answered affirmatively. This turned out to be a strongargument against Berkeley’s theory of vision. Others, ThomasBrown for instance, were of the opinion that the visual behaviour ofbabies could be compared with that of a blind person who had beenoperated upon and made to see. They were convinced that in both casesseeing has to be learned, and that Molyneux’s question had,therefore, to be answered in the negative.

Wheatstone’s discovery that the perception by sight of the thirddimension of space is immediate, was used as a reason for answeringMolyneux’s question affirmatively. The discovery was alsoregarded as disproving Berkeley’s theory of vision.

The data concerning the sight of patients who had been operated uponfor cataracts, and of young animals and infants, were used as evidencein the debate concerning the question of whether the perception ofspace is innate or acquired. Although Molyneux’s problem wasfrequently discussed in this debate, there was still no agreement onthe right solution to it.

5. Modern Approaches

During the course of the twentieth century, the main interest inMolyneux’s problem has been historical. Biographers andcommentators dealing with well-known philosophers have analysed thesolutions they proposed for it. Molyneux’s problem has alsoturned up frequently in textbooks and general histories of psychology,ophthalmology, neurophysiology, etcetera (and also in publications ondiverse disciplines, like mathematics, architecture, literature, artsand sports). A few authors have written brief and incomplete historiesof the problem. Degenaar (1996) has written a comprehensive survey ofthe history of the discussion about Molyneux’s problem. Riskin(2002) described Molyneux’s problem in the wider context of theEnlightenment.

Philosophers, psychologists and other scientists have also tried tosolve the Molyneux problem by making use of alternative approaches,both old and new. They have, for example, made use of various accountsof recovery from early blindness. As was to be expected, these provedto be as problematic and inconclusive as were their predecessors inthe eighteenth and nineteenth centuries.

The Molyneux problem has also been tackled by methods more amenable toexperimental control than is possible in clinical studies, namely byrearing animals in darkness. Visual deprivation experiments have shownthat during the development of the visual system there is a certaincritical period in connection with the presentation of light patterns.During this period, changes brought about by deprivation can bereversed. If exposure to light is postponed for too long, however, thedevelopment of normal visual mechanisms will be extremely difficult,if not impossible. Although the results of deprivation experiments arenot relevant to the solution of Molyneux’sproblem—Molyneux supposed that his blind man had a good visualsystem, whereas that of deprived animals is abnormal—they havebeen used as evidence for Locke’s position.

A different approach to Molyneux’s problem involves the use ofsensory substitution devices, developed in the context of corporealmobility or reading (Morgan, 1977). Learning how to use sensorysubstitution systems has been considered a good approximation toMolyneux’s problem, since such systems present informationnormally handled by one modality, such as vision, to another sense,typically audition or touch, using forms of coding novel to the user.Experiments with sensory substitution systems show that subjects needsome time to learn to distinguish and identify objects, and this hasbeen interpreted as a confirmation of the position of Molyneux andLocke. Some researchers have stressed the fact that a sensory aid isnot, strictly speaking, a new modality, and that to learn to use suchdevices is only an approximation to Molyneux’s problem,depending as it does upon the raising of similar issues.

Another variation of Molyneux’s problem was suggested by Evans(1985). He wondered whether the visual cortex of a patient withcongenital blindness could be electrically stimulated in such a waythat the patient experiences a pattern of light flashes (phosphenes)in the shape of a square or circle. This question has beeninvestigated experimentally, but the results do not provide a finalanswer to Molyneux’s question (see Jacomuzzi, Kobau and Bruno2003 for discussion).

More recently, Gallagher (2005, ch. 7) argued that moderndevelopmental psychology and neurophysiology suggest thatLocke’s reaction to Molyneux’s question was right, but forthe wrong reasons.

A more or less straightforward attempt to answer Molyneux’squestion empirically has been carried out during the last decade. Onereason that Molyneux’s problem could be posed in the first placeis the dearth of human subjects who gain vision after extendedcongenital blindness. It has been estimated that less than twentycases have been found in the last 1000 years (Valvo 1971). In Westerncountries the vast majority of cases of curable congenital blindnessare detected in infancy and treated as early as possible. However,many congenitally blind children in developing countries often do notreceive treatment despite having curable conditions because ofinadequate medical services. In 2003, Pawan Sinha set up a program inIndia as a part of which he treated five patients, aged from 8 to 17years, that almost instantly took them from total congenital blindnessto fully seeing. This provided an opportunity to answerMolyneux’s problem empirically. Based on this study, it wasconcluded that the answer to Molyneux’s question is likelynegative. Although after restoration of sight, the subjects coulddistinguish between objects visually as effectively as they would doby touch alone, they were unable to form the connection between objectperceived using the two different senses. The results of thetouch-to-vision tests were barely better than if the subjects hadguessed. However, such cross-modal mappings developed rapidly, in thecourse of a few days (Held,et al., 2011).

A fruitful tendency is taking Molyneux’s problem to be a clusterof subproblems^[3] or generating different versions of or variations on Molyneux’sproblem (e.g. Glenney, 2013 and Matthen and Cohen, 2020).

A valuable contribution to the discussion about Molyneux’sProblem is Ferretti and Glenney (2021), a collection of one poem andtwenty essays that explore the long-standing issues Molyneux’sproblem presents to philosophy of mind, perception and the senses. Itconsiders the question from an interdisciplinary angle, examines itspre-history, and perspectives from religion and disability. The essaysare arranged around five criticisms: (1) Molyneux’sappropriation of the question from another source; (2) theencouragement of bias against people with blindness, a social failurecalled ocularism; (3) a lack of specificity resulting in ambiguity asto what might count as a satisfying answer; (4) a crude generalitythat belies the underlying complexity of vision and touch; and (5) theincapability to be experimentally testable, though presumably designedto be so (Ferretti and Glenney, 2021, p. 2).

6. Conclusion

The history of the issues surrounding Molyneux’s question showsthat the question was not as easy to answer as Molyneux himself mayhave assumed. On the contrary, there is no problem in the history ofthe philosophy of perception that has provoked more thought than theproblem that Molyneux raised in 1688. In this sense, Molyneux’sproblem is one the most fruitful thought-experiments ever proposed inthe history of philosophy, which is still as intriguing today as whenMolyneux first formulated it more than three centuries ago.

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