The validation of sensation

If, after Descartes, the issues raised around blindness for Locke and Berkeley originate in philosophical inquiry and speculative epistemology, then the results of surgical intervention lie within scientific experimentation. Locke's empiricism was taken up in Europe as a challenge to the entrenched rationalism of Descartes, and a new emphasis on the centrality of experience and sensation was kickstarted by Voltaire in exile, and developed into a fully fledged sensationism through Condillac. It is some measure of the ‘fruitfulness’ of the Molyneux question, thinks Ernst Cassirer in his monumental study The Philosophy of the Enlightenment, that it continued to stimulate responses in France several decades later. Voltaire in his Éléments de la philosophie de Newton offered ‘an extensive exposition of the problem’, and Condillac apparently declared that ‘it contains the source and key to all modern psychology’ (Cassirer 1979: 109). Cheselden's 1728 report to the Royal Society in London provided further stimulus to the French intellectual imagination. After Voltaire introduced a French readership to Cheselden's case study through the Elements, in successive years there followed further discussion of the role of the senses in the production of knowledge, including Condillac's Essai sur l’origine des connaissances humaines [‘An essay on the origin of human knowledge’] (1746) and, in a revised form, Traité des sensations [‘Treatise on the sensations’] (1754); Diderot's Lettre sur les aveugles à l’usage de ceux qui voient [‘Letter on the blind for the use of those who see’] (1749); and George Buffon's Histoire naturelle, générale et particulière [‘Natural history of man’] (1749). A chapter in La Mettrie's Histoire naturelle de l’âme [‘Natural history of the soul’] (1745) was entitled ‘Stories that confirm that all ideas come from the senses’, simultaneously invoking the familiar Peripatetic axiom while reaffirming the centrality of sensation in epistemological inquiry. In the wake of new scientific and surgical discoveries, French commentators such as the sensationists often considered the fact that sensations had a source outside the body to be an emotional matter, but also that there was no substantial separation between the emotional and the cognitive aspects (Riskin 2002: 49). After Cheselden, sensation and sensationism in France were going to take a radical new trajectory.