## 1. Molyneux's Formulation of the Problem



As is apparent from both his writings and his lectures, Molyneux was
highly interested in optics and in the psychology of sight. To some
extent this simply reflects the general attitude of his time: optics
was a subject that was then engaging the attention of a number of
leading scientists. His interest also had a more personal background,
however, for his wife had lost her sight in the first year of their
marriage. The immediate cause of his formulating the problem and
sending it to Locke is to be found in Locke's French extract of
*An Essay Concerning Humane Understanding*, published in 1688
in the *Bibliotheque Universelle & Historique*. In
this extract Locke distinguished between ideas we acquire by means of
one sense and those we acquire by means of more than one sense. He
maintained that someone who lacks a sense will never be able to
acquire the ideas pertaining to it. A blind man, for example, will
never be able to have any idea of colour. Among the ideas we are able
to acquire by means of a combination of senses, Locke reckoned those
of space, rest, motion and figure. Molyneux's problem had to do
with the last of these. Molyneux was probably inspired by
Locke's exposition of the ideas of persons born blind and the
ideas which can be acquired by means of both sight and touch. He was,
moreover, a great admirer of Locke. (Although earlier we suggested
that Molyneux might have been inspired by Ibn Tufail's
twelfth-century philosophical novel *Hayy ibn Yaqdhan*, which
had just been published in Latin (1671) and English (1674) and also
had an influence on Locke, there seems to be no indication that
Molyneux read Ibn
 Tufail.)[1]



On Saturday 7 July 1688 William Molyneux wrote a letter to John Locke
setting out for the first time his problem concerning the person born
blind:



> 
> 
> Dublin July. 7. 88
> 
> 
> 
> *A Problem Proposed to the Author of the Essai Philosophique
> concernant L'Entendement* 
> 
> 
> 
> A Man, being born blind, and having a Globe and a Cube, nigh of the
> same bignes, Committed into his Hands, and being taught or Told, which
> is Called the Globe, and which the Cube, so as easily to distinguish
> them by his Touch or Feeling; Then both being taken from Him, and Laid
> on a Table, Let us Suppose his Sight Restored to Him; Whether he
> Could, by his Sight, and before he touch them, know which is the Globe
> and which the Cube? Or Whether he Could know by his Sight, before he
> stretch'd out his Hand, whether he Could not Reach them, tho
> they were Removed 20 or 1000 feet from Him?
> 
> 
> 
> If the Learned and Ingenious Author of the Forementiond Treatise think
> this Problem Worth his Consideration and Answer, He may at any time
> Direct 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, a
couple of years later, after the two men had started an amicable
correspondence, Molyneux returned to his problem. This time with
success. In his letter, dated 2 March 1693, Molyneux presented Locke
with his problem, though in a somewhat altered form, asking Locke if
he could perhaps find some place in his *Essay* to say
something about it. This time Locke reacted with enthusiasm:
"Your ingenious problem will deserve to be published to the
world." From the second edition of his *Essay* (that of
1694) Locke included Molyneux's problem in his work and thereby
made it accessible to a wider audience:



> 
> Suppose a Man born blind, and now adult, and taught by his touch to
> distinguish between a Cube, and a Sphere of the same metal, and nighly
> of the same bigness, so as to tell, when he felt one and
> t'other; which is the Cube, which the Sphere. Suppose then the
> Cube and Sphere placed on a Table, and the Blind Man to be made to
> see. Quaere, Whether by his sight, before he touch'd them, he
> could now distinguish, and tell, which is the Globe, which the Cube.
> 



In this formulation Molyneux's problem attracted the attention
of lots of philosophers and other men of learning, such as Berkeley,
Leibniz, Voltaire, Diderot, La Mettrie, Helmholtz and William
James. 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 impossible
that a man born blind should be able to acquire sight. They regarded
Molyneux's problem as a kind of thought-experiment, which was to
be dealt with by ratiocination alone. The arguments put forward were
usually concerned with the relation between visual and tactual
sensations or between visual and tactual notions of the form of
objects.



All these philosophers assumed that the visual and tactual sensations
of an object differ from each other, but there was no agreement
concerning 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 and
perceived directly, while yet others, such as Molyneux and Locke,
thought that it is necessary and learned by experience. Opinions were
also divided concerning the relation between visual and tactual
notions of objects. Some philosophers defended the position that the
visual and tactual notions of a globe differ from one another, and can
only be related by either experience or reason (the latter view was
defended by Reid). Others believed that the visual and the tactual
notion of a globe are actually the same, or have something in common
which is either observed directly (Boullier and Hutcheson) or inferred
by reason (Leibniz).



Investigating how the different positions correlate with the answers
given to Molyneux's question, one can conclude as follows.
Empiricists such as Molyneux, Locke and Berkeley answered in the
negative. More rationalist philosophers such as Synge, Lee and Leibniz
gave an affirmative answer. There was no unanimous solution, amongst
others because Molyneux's problem was interpreted in different
ways. Some philosophers thought that the man born blind had to answer
directly, while others were of the opinion that he should be able to
make use of his memory and reason, and that he should be at liberty to
view all sides of the objects by walking around them. Some
philosophers believed that the question implied that the man should be
told in advance that he would be presented with a globe and cube,
whereas others thought that he should not be provided with this
information.


## 3. The First Experimental Data



Discussion concerning Molyneux's problem took a new turn once
the English surgeon and anatomist William Cheselden (1688-1752)
published an account of what a congenitally blind person had seen
after his cataracts had been removed (1728). The publication led
philosophers to regard the Molyneux problem no longer as a simple
thought-experiment, but as a question which could be answered by
experimentation.



In his account, Cheselden noted that when the boy--who recently
has been identified as Daniel Dolins--was first able to see, he
did not know the shape of a thing and could not recognize one thing
from another, regardless of how different in shape or magnitude they
 were.[2]
 Some philosophers thought that Cheselden's observations were
unequivocal and that they confirmed the hypothesis that a blind man
restored to sight would not be able to distinguish objects and would
have to learn to see. Most of these philosophers, we might mention
Voltaire, Camper and the elder Condillac as examples, were adherents
of Berkeley's theory of vision, which had predicted a similar
outcome.



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



Those who criticised the significance of Cheselden's account in
this way (most of them were French *philosophes*) made
proposals as to how to avoid the problems mentioned. They suggested
that one should prepare the patient carefully for the operation and
for the interrogation, that one should allow his eyes time to recover
from the operation and that one should give him the opportunity to
exercise his eyes in darkness. What is more, one should avoid asking
leading questions.



Some philosophers were even more radically critical of operations like
that performed by Cheselden. Merian, for example, noticed that
Cheselden's observations, like all observations of blind people
whose cataracts have been extracted, present difficulties because
cataracts do not cause complete blindness and complete blindness
cannot be cured. It could not be concluded from this that
Molyneux's problem could not be solved experimentally, however,
for it could be maintained that patients operated upon for cataracts
are directly relevant to the solution of it. They are unable to
perceive form before they are operated upon, and the essential issue
at stake when posing Molyneux's problem is the ability to
distinguish and name forms. This is a point of view which was taken by
many philosophers.



## 4. Empirical Approaches in the Nineteenth Century



About 1800 several developments occurred which justify the speaking of
a new period in the history of Molyneux's problem. New accounts
of patients operated on for cataracts were published, and shed fresh
light on the issue. Whereas Cheselden had only noticed what his
patient observed in more or less natural circumstances, later
ophthalmologists performed experiments which showed whether their
patients were able to see form, size, distance, etc. Some, such as
Franz and Nunneley, were especially interested in Molyneux's
problem as such, and performed experiments with the prescribed globe
and cube. Some of the reports were in agreement with that of
Cheselden, others conflicted with it. The cases could not easily be
compared, however, since the pre- and post-operative circumstances
differed to such a great extent. As one might have expected, an
extended scale of possible solutions to the Molyneux problem was
brought under consideration.



What is more, specialists also began to consider observations
concerning the sight of newly born animals and babies when discussing
Molyneux's problem. Some of those doing research in the field,
such as Adam Smith and Johannes Muller, supposed that the sight
of young animals could be compared with that of a person who had been
made to see. The fact that certain animals see objects at a distance
as soon as they are born suggested that Molyneux's question
could be answered affirmatively. This turned out to be a strong
argument against Berkeley's theory of vision. Others, Thomas
Brown for instance, were of the opinion that the visual behaviour of
babies could be compared with that of a blind person who had been
operated upon and made to see. They were convinced that in both cases
seeing 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 third
dimension of space is immediate, was used as a reason for answering
Molyneux's question affirmatively. The discovery was also
regarded as disproving Berkeley's theory of vision.



The data concerning the sight of patients who had been operated upon
for cataracts, and of young animals and infants, were used as evidence
in the debate concerning the question of whether the perception of
space is innate or acquired. Although Molyneux's problem was
frequently discussed in this debate, there was still no agreement on
the right solution to it.


## 5. Modern Approaches



During the course of the twentieth century, the main interest in
Molyneux's problem has been historical. Biographers and
commentators dealing with well-known philosophers have analysed the
solutions they proposed for it. Molyneux's problem has also
turned up frequently in textbooks and general histories of psychology,
ophthalmology, neurophysiology, etcetera (and also in publications on
diverse disciplines, like mathematics, architecture, literature, arts
and sports). A few authors have written brief and incomplete histories
of the problem. Degenaar (1996) has written a comprehensive survey of
the history of the discussion about Molyneux's problem. Riskin
(2002) described Molyneux's problem in the wider context of the
Enlightenment.



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



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



A different approach to Molyneux's problem involves the use of
sensory substitution devices, developed in the context of corporeal
mobility or reading (Morgan, 1977). Learning how to use sensory
substitution systems has been considered a good approximation to
Molyneux's problem, since such systems present information
normally 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 need
some time to learn to distinguish and identify objects, and this has
been interpreted as a confirmation of the position of Molyneux and
Locke. Some researchers have stressed the fact that a sensory aid is
not, strictly speaking, a new modality, and that to learn to use such
devices 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 with
congenital blindness could be electrically stimulated in such a way
that the patient experiences a pattern of light flashes (phosphenes)
in the shape of a square or circle. This question has been
investigated experimentally, but the results do not provide a final
answer to Molyneux's question (see Jacomuzzi, Kobau and Bruno
2003 for discussion).



More recently, Gallagher (2005, ch. 7) argued that modern
developmental psychology and neurophysiology suggest that
Locke's reaction to Molyneux's question was right, but for
the wrong reasons.



A more or less straightforward attempt to answer Molyneux's
question empirically has been carried out during the last decade. One
reason that Molyneux's problem could be posed in the first place
is the dearth of human subjects who gain vision after extended
congenital blindness. It has been estimated that less than twenty
cases have been found in the last 1000 years (Valvo 1971). In Western
countries the vast majority of cases of curable congenital blindness
are detected in infancy and treated as early as possible. However,
many congenitally blind children in developing countries often do not
receive treatment despite having curable conditions because of
inadequate medical services. In 2003, Pawan Sinha set up a program in
India as a part of which he treated five patients, aged from 8 to 17
years, that almost instantly took them from total congenital blindness
to fully seeing. This provided an opportunity to answer
Molyneux's problem empirically. Based on this study, it was
concluded that the answer to Molyneux's question is likely
negative. Although after restoration of sight, the subjects could
distinguish between objects visually as effectively as they would do
by touch alone, they were unable to form the connection between object
perceived using the two different senses. The results of the
touch-to-vision tests were barely better than if the subjects had
guessed. However, such cross-modal mappings developed rapidly, in the
course of a few days (Held, *et al*., 2011). 



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



A valuable contribution to the discussion about Molyneux's
Problem is Ferretti and Glenney (2021), a collection of one poem and
twenty essays that explore the long-standing issues Molyneux's
problem presents to philosophy of mind, perception and the senses. It
considers the question from an interdisciplinary angle, examines its
pre-history, and perspectives from religion and disability. The essays
are arranged around five criticisms: (1) Molyneux's
appropriation of the question from another source; (2) the
encouragement of bias against people with blindness, a social failure
called ocularism; (3) a lack of specificity resulting in ambiguity as
to what might count as a satisfying answer; (4) a crude generality
that belies the underlying complexity of vision and touch; and (5) the
incapability to be experimentally testable, though presumably designed
to be so (Ferretti and Glenney, 2021, p. 2).


## 6. Conclusion



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