Feature Endeavour Vol.32 No.4

Cartesian visions

Patricia Fara

Clare College, Cambridge, CB2 1TL, UK

Few original portraits exist of Rene Descartes, yet histheories of vision were central to Enlightenmentthought. French philosophers combined his emphasison sight with the English approach of insisting that ideasare not innate, but must be built up from experience. Inparticular, Denis Diderot criticised Descartes’s views bydescribing how Nicholas Saunderson – a blind physicsprofessor at Cambridge – relied on touch. Diderot alsomade Saunderson the mouthpiece for some hereticalarguments against the existence of God.

‘What is an idea?’ asked Voltaire? Replying immediately tohis own question, this eminent French philosopherdescribed an idea as an image ‘that paints itself in mybrain. . .I’ve ideas only because I’ve images in my head1’.Strongly influenced by Rene Descartes (1596–1650), Vol-taire equated knowing with seeing, as if the mind has aninternal eye that can gaze upon the impressions storedwithin it. Descartes had made vision central to his naturalphilosophy. As well as enthusing about the wondersrevealed by telescopes and dissecting an ox eye acquiredfrom his local butcher, Descartes declared that of all thesenses, ‘sight is the most comprehensive and the noblest2’.According to him, eyes alone are not enough for seeingeffectively – people are born with a mental framework thathelps them understand what they are looking at. Descar-tes’s belief in such innate ideas inspired him to sweep awayeverything that he had been taught and build up his ownphilosophical system from scratch.

Despite his emphasis on vision, Descartes posed for veryfew portraits. He may not even have sat for the iconicpainting by Franz Hals, which was often copied and pro-vided the source of an engraving showing Descartes atwork (Figure 1). Quill pen in his hand, Descartes kicksaway Aristotle, classical fount of wisdom, in favour ofmaking his own observations. This is no traditional scho-lar’s study. As though visually interpreting Descartes’rejection of his predecessors, the artist here presentshim in the act of writing his own book from his ownthoughts, working in a sparse room bereft of the usuallearned tomes left open for easy reference.3

Dressed in neat but simple clothes, this is the man whohad sufficient self-confidence to lock himself away in soli-tary contemplation and conclude that he had a solid start-ing-point for his new philosophy: ‘I think, therefore I am’.

Corresponding author: Fara, P. (pf10006@cam.ac.uk)1 Quoted Jay, M. (1993) Downcast Eyes: The Denigration of Vision in Twentieth-

Century French Thought, University of California Press, (Berkeley) p. 83 (fromVoltaire’s Philosophical Dictionary)..

2 Quoted Jay, p. 71 (from Descartes’s La Dioptrique)..3 Gaskell, R. (2007) Scientific and Medical Portraits, Warboys: Roger Gaskell Rare

Books, pp. 33–44.Available online 4 November 2008.

www.sciencedirect.com 0160-9327/$ – see front matter � 2008 Elsevier Ltd. All rights reserve

By envisaging his soul as being separate from his body,Descartes could imagine himself as a detached spectatorlooking upon the physical world, rather than as an activeparticipant whose viewpoint must inevitably be subjective.Yet although Descartes’s views dominated French thoughtfor the next 100 years, his Enlightenment followers werealso impressed by the insistence of English philosophersthat information about theworldmust be obtained throughthe senses.

After a period of forced exile, Voltaire became a particu-larly enthusiastic campaigner for England’s famous scho-lars, such as John Locke and Isaac Newton. In his Anglo-French version of the newborn brain as a blank slate, theabstract ideas painted inside people’s minds were not thereat birth, but are composed from perceptions that havepoured in throughout their life. To back up his claim thatDescartes was wrong about innate concepts, Voltaire pro-duced experimental evidence. Like many eighteenth-cen-tury philosophers, he wanted to answer what hadoriginally been a hypothetical question: if the power ofsight were suddenly restored to blind people, would they beable to identify objects they had formerly known only bytouch? In England, he heard about a young man whosecataracts had been surgically removed. Although he could

Figure 1. A line engraving of Rene Descartes by C Hellemans.

d. doi:10.1016/j.endeavour.2008.09.002

Figure 2. An oil painting of Nicholas Saunderson by John Vanderbank, painted in 1718 or 1719. Photograph by Tom Russell. Courtesy of the University of Cambridge.

Feature Endeavour Vol.32 No.4 127

now see for the first time, he could not immediately dis-tinguish shapes, sizes, and distances, but had to learn howto perceive the world with his eyes rather than with hishands, ears, and nose. Voltaire used this real-life casestudy to corroborate the English view that abstract ideasare not inborn but are acquired through experience.

The most controversial discussion of blindness was byDenis Diderot, co-editor of the French Encyclopedie, whoseLetter on the Blind for the Use of Those Who See (1749)earned him a spell in prison for its heretical comments onGod. To act as his mouthpiece, Diderot chose NicholasSaunderson, the Lucasian professor of mathematics at

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Cambridge. Saunderson had lost his eyes as well as hissight after a childhood attack of smallpox (Figure 2).Nevertheless, he lectured on astronomy and Newtoniannatural philosophy – including optics – and also wrote abook on algebra, which was published shortly after hisdeath for the financial benefit of his widow. Saundersonwas painted by a distinguished artist, John Vanderbank,whose earlier portrait of Isaac Newton was widely repro-duced as the frontispiece of the Principia’s famous thirdedition. By deciding to show Saunderson feeling around anarmillary sphere, Vanderbank foregrounded the import-ance of touch in this scholar’s daily life.

128 Feature Endeavour Vol.32 No.4

DiderotusedSaunderson’sphysicalandmentaldexterityto counter Descartes’s insistence on the primacy of sight. Asheput it, ‘If ever aphilosopher, blindanddeaf fromhis birth,were to construct a man after the fashion of Descartes...hewould put the seat of the soul at the fingers’ ends, for it isfrom these that the greater part of the sensations and all hisknowledge are derived4.’ Making his admiration clear,Diderot described in detail how Saunderson had inventeda method of representing numbers by arranging pins ofvarious shapes in square patterns. By moving his fingersover this device, Saunderson could not only perform calcu-lations rapidly and accurately, but could also formulategeometrical proofs.

According to Diderot, just as Saunderson interpretedinvisible phenomena by converting them into tangiblecounting pins, so the universe could be decoded throughmathematics. Saunderson also provided him with aconvenient spokesman for atheism. In a fictionalisedconversation, Diderot imagined Saunderson lying on his

4 Diderot, D. (1999) Thoughts on the Interpretation of Nature and Other Philoso-phical Works, Clinamen Press, (Manchester) p. 159 (from Letter on the Blind).

5 Diderot, D. (1999) Thoughts, p. 172 (from Letter on the Blind).6 Diderot, D. (1999) Thoughts, p. 176 (from Letter on the Blind).

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death bed but still capable of lucidly refuting a clergyman’sarguments for the existence of God. Reducing his audienceto tears by pointing to his own disability, Saundersonrejected his clerical visitor’s invitation to admire the won-ders of nature, and exclaimed: ‘If you want to make mebelieve in God you must make me touch Him5’. Writing asSaunderson, Diderot argued that it is impossible for peopleto be certain whether or not imperfection exists elsewherein space or in time. Just as a short-lived antmay not realisethat humans are mortal, so too, we cannot be sure that theuniverse is eternal.

Reverting to his own voice, Diderot castigated those whoinfer a divine creator from the marvels of nature. With afine rhetorical if sacrilegious flourish, he declaimed: ‘theylead the life of the blind, and Saunderson died as if he knewthe light6’. A Newtonian propagandist, Diderot analysedblindness to refute some Cartesian views, yet he alsodenied the God who was so central to Newton’s outlookon life.