Descartes: A Biography

C CUNYB/Clarke     December, :

 Descartes: A Biography

similar to the child’s sensation (xi.). The external cause of the sensation

is nothing other than the motion of the feather when it touches the lips,

butthis is perceived by the child as a tickling sensation. There is therefore

no reason to believe that there is a ‘tickling quality’ in the feather that

resembles the child’s sensation. Another argument is that words succeed

in communicating their meanings to those who speak the language used,

butthere is no reason to think that the words actually resemble the realities

to which they refer. Descartes argues: ‘Now if words...are enough to

make us think about things that do not resemble them in any way, why

is it not possible that nature may also have established a particular sign

that would make us have the sensation of light, even though such a sign

contains nothing in itself that resembles that sensation?’ (xi.)

With these and similar arguments, Descartes helped open the epistemic

gap–between our subjective sensations and the external realities that cause

them – that became one of the hallmarks of the Scientific Revolution. He

later applied the same argument to so-called internal sensations, such

as the sensation of hunger or pain. The significance of these apparently

simple conclusions was that they opened up an ‘appalling vista’ for tradi-

tional science. Once this question was raised, it was impossible to adopt

the na ̈ıve assumption of the scholastic tradition that our senses cannot err

when they are applied to appropriate objects. It simply could no longer be

assumed that the world that we experience, externally or internally, resem-

bles our perceptions. Since we cannot legitimately project our sensory

experiences onto reality, we have no alternative but to construct hypothe-

ses about the kinds of realities that are likely to cause the sensations that we

experience.

This ground-breaking initiative in theory of knowledge led to an equally

original insight into the nature of explanation, although it was some

years before Descartes made explicit its full implications. Where scholas-

tic philosophers had assumed that a burning piece of wood must have

properties such as the ‘quality’ of heat or light and the ‘form’ of burn-

ing, Descartes concluded that these were mere projections onto exter-

nal realities of the subjective character of our sensations. He suggested,

instead, that we imagine in burning wood a large number of very small,

fast-moving particles, so that the conversion of the burning wood into

ashes and the emission of light, smoke, and so on. are merely observ-

able results of events that are too microscopic to observe with the naked

eye. ‘On condition simply that you grant me that there is some power