Popularly known as the father of modern philosophy, René Descartes won that title ostensibly by rejecting traditional modes of intellectual inquiry largely associated with commentary on prior texts, and replacing them with the first attempt at a kind of radical phenomenology. The drama of this attempt is conveyed autobiographically in the first of his six Meditations, in which he describes the strenuous process of sloughing off received ideas and subjecting everything he thinks he knows to doubt. He finds it tough going, and repeatedly realizes that he has fallen back on some "long standing opinions" that "take advantage of his credulity." His last ditch effort to subject all possible knowledge to doubt comes in the form of a figure he calls an evil genius or demon, in Latin a genius malignus, "supremely powerful and clever, who has directed his entire effort at deceiving me. I will regard the heavens, the air, the earth, colors, shapes, sounds, and all external things as nothing but the bedeviling hoaxes of my dreams, with which he lays snares for my credulity."
This device leads him, of course, at the outset of the second meditation to fall upon the distinction that still bears his name, the dualism between what can be doubted—namely the accuracy of my knowledge about the extended world—and what cannot be—the fact that there is some thing that is doing the doubting, that is thinking, having that knowledge, true or false, about the extended world: "And let him do his best at deception, he will never bring it about that I am nothing so long as I shall think that I am something."
The distinction Descartes' experiment engendered is basic to modern thought. It animates the entire history of epistemology, from Kant through to the phenomenological tradition prior to Heidegger; it challenges a whole counter-tradition starting with Spinoza and leading to Deleuze and contemporary affect theory; it is the core problem of the subdiscipline of academic philosophy devoted to the mind-body problem. But far more crucially, it infiltrates in a variety of guises modern science and political discourse as well: in the form of the researcher who strives to derive reliable laws from the messy influx of experimental data, necessarily minimizing human error and bias as he goes; in the idea of an abstract citizen who stands on equal footing with all other members of the same state, in patent contradiction to the blatant real inequalities that beset the people living under the aegis of that sovereign power.
In its simplest form, then, the modern world was born with the speculation that I can be wrong about everything I know while still being me; the possibility that everything about my world could be a show, put on for my benefit; that the people I engage with could be part of it; that everything could appear to be perfectly real and perfectly natural, but that it could all be false. This was emphatically not the idea behind Plato's cave allegory; in fact, I know of no other formulation prior to Descartes of this exact idea, an idea that has proven so influential for modern thought in general. No previous philosophical formulation, that is.
While it has hardly constituted a cottage industry, in the 400 years since Cervantes published Don Quixote and the almost 400 since Descartes published his Meditations, a few scholars have noted the similarities between Descartes' evil genie and the enchanter who bedevils Don Quixote's world, popping up as the perfect rationalization for every instance when Quixote's assertions are disproven, when reality fails to deliver on his illusory expectations. Descartes seems to acknowledge having read Don Quixote in his Discourse on Method, where he warns readers of falling under the influence of "fables, tales of chivalry, and even of the most faithful histories…lest they conceive of plans that surpass their abilities." The first French translations of Don Quixote were published in 1614 and 1618, and the two books were translated anew by François de Rosset and published in 1639, two years before Descartes published his Meditations. But there is no need to yearn for greater evidence of a direct influence; by that time every intellectual in Europe was aware of Cervantes' creation; his influence was impossible to avoid.
It is crucial to add that this is not merely an issue of noting the presence of a similar figure in two books. While the influence of witches was widely acknowledged as a potentially vexing obstacle for determining responsibility in the popular consciousness of the time, the idea of an enchanter with the power to make the same world look entirely different to me as it does to another person is a brilliant and outrageous hyperbole, and was as much at the core of Cervantes' artistic innovation as it was central to Descartes' project and the subsequent philosophical discourse of modernity. Here's how Don Quixote formulates the function of the encantador maligno in a moment of frustration at his and Sancho's continued disagreements over whether what Quixote wears on his head is in fact the fabled helmet of Mambrino, or merely a well-used barber's basin:
"Well, Sancho, by the same oath you swore before, I swear to you," said Don Quixote, "that you have the dimmest wits that any squire in the world has or ever had. Is it possible that in all the time you have traveled with me you have not yet noticed that all things having to do with knights errant appear to be chimerical, foolish, senseless, and turned inside out? And not because they really are, but because hordes of enchanters always walk among us and alter and change everything and turn things into whatever they please, according to whether they wish to favor us or destroy us; and so what seems to you a barber's basin seems to me the helmet of Mambrino, and will seem another thing to someone else.
Here the translation I chose actually dissimulates an even more revealing coincidence with Descartes work. What Edith Hamilton renders as chimerical was, in the original Spanish, a noun, quimera. This would be of no importance were it not for the fact that 36 years later, as Descartes puzzles over how to salvage the possibility of certain knowledge from the hypothetical possibility that his perception of the world is manipulated by a great deceiver, he finds solace in this argument: "Now as far as ideas are concerned, if they are considered alone and in their own right, without being referred to something else, they cannot, properly speaking, be false. For whether it is a she-goat or a chimera that I am imagining, it is no less true that I imagine the one that the other." Again, we are free to remain entirely skeptical as to the coincidence of that mystical beast's appearance, especially given that chimeras had been used metaphorically since the late sixteenth century to signify unreal products of theimagination.
The point remains that Descartes is seeking his ground in exactly the same place the novel situates our own ground: as long as we know that what things appear to be, chimeras, is secondary to our knowledge that they appear at all or can appear in various ways to various people, then we have the security of our own existence intact. The hordes of enchanters that turn things into whatever they please are unable to turn you, me, or someone else, that it, those to whom the world appears in one way or the other, into something other than we are. It is for that very reason that we persist through the changes around us to argue our positions; we can disagree on the variety of our perceptions only if we are secure in the identity of the self who perceives.