Excerpted from Jess Keiser’s review of Bedeviled: A Shadow History of Demons in Science by Jimena Canales:
Writing in the mid-17th century, the French philosopher René Descartes realized that in order “to establish anything at all in the sciences that was stable and likely to last,” he first needed to lash himself to a single point of certainty in a roiling sea of doubt.
To test the strength of his position, Descartes imagined the workings of an evil entity– a malignum genium, or evil genius– capable of creating an entirely illusory but completely convincing artificial world. Someone ensnared by Descartes’ malevolent being is bound to question external reality– and even their own body– since, theoretically, the sky’s color or the warmth of one’s skin could be deceptions devised by this demon.
Although its powers appeared absolute, Descartes’ demon couldn’t corrode all sources of certainty. Since this “genius” needed a target for its tricks– an underlying consciousness that could be deceived in the first place–its victims could at least be sure they existed. Hence, Descartes’ absolute trust in the formula of his famous “cogito”: I think, therefore I am.
I had heard the quote, but never knew the context
You can read the full review at the Washington Post, HERE.