In his Meditations Descartes tells us that he initially thought error might be avoided if he withheld assent “no less carefully from what is not plainly certain and indubitable than from what is obviously false.” For example, he thinks it plainly certain and indubitable that he is “sitting by the fire, wearing a winter cloak, holding this paper in my hands, and so on.” And yet even what is “plainly certain and indubitable” can be doubted. “I will suppose, then, not (...) that there is a supremely good God, the source of truth; but that there is an evil spirit, who is supremely powerful and intelligent, and does his utmost to deceive me.” Such a deceiver can spin illusions that appear indubitably real and true—of hands, fire, cloak, paper—and not only when there are none present in any particular case but even where there are none at all in any case. “I will suppose that sky, air, earth, colors, shapes, sounds and all external objects are mere delusive dreams, by means of which he lays snares for my credulity.”2 The deceiver hypothesis is the most difficult skeptical doubt Descartes must surmount in the remaining Meditations. I say the deceiver hypothesis, and for Descartes the deceiver is a mere possibility, raised so as to motivate the reconstitution of knowledge that follows. That there might be a powerful deceiver is itself a threat to knowledge for Descartes. Indeed even the possibility of an evil deceiver is so powerful a threat that Descartes must do nothing less than prove God’s existence to reestablish certainty. It is only at the end of his Meditations that Descartes can say, as if looking back on a hysterical moment, that the evil deceiver idea was “exaggerated” and “ridiculous.”3.. (shrink)