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Descartes: Starting with Doubt

For a more complete formal presentation of this foundational experience, we must turn to the Meditationes de prima Philosophia (Meditations on First Philosophy) (1641), in which Descartes offered to contemporary theologians his proofs of the existence of god and the immortality of the human soul. This explicit concern for religious matters does not reflect any loss of interest in pursuing the goals of science. By sharply distinguishing mind from body, Descartes hoped to preserve a distinct arena for the church while securing the freedom of scientists to develop mechanistic accounts of physical phenomena. In this way, he supposed it possible to satisfy the requirements of Christian doctrine, but discourage the interference of the church in scientific matters and promote further observational exploration of the material world.

The arrangement of the Meditations, Descartes emphasized, is not the order of reasons; that is, it makes no effort to proceed from the metaphysical foundations of reality to the dependent existence of lesser beings, as Spinoza would later try to do. Instead, this book follows the order of thoughts; that is, it traces the epistemological progress an individual thinker might follow in establishing knowledge at a level of perfect certainty. Thus, these are truly Meditations: we are meant to put ourselves in the place of the first-person narrator, experiencing for ourselves the benefits of the philosophical method.

The Method of Doubt

The basic strategy of Descartes's method of doubt is to defeat skepticism on its own ground. Begin by doubting the truth of everything—not only the evidence of the senses and the more extravagant cultural presuppositions, but even the fundamental process of reasoning itself. If any particular truth about the world can survive this extreme skeptical challenge, then it must be truly indubitable and therefore a perfectly certain foundation for knowledge. The First Meditation, then, is an extended exercise in learning to doubt everything that I believe, considered at three distinct levels:

  1. Perceptual Illusion

    First, Descartes noted that the testimony of the senses with respect to any particular judgment about the external world may turn out to be mistaken. (Med. I) Things are not always just as they seem at first glance (or at first hearing, etc.) to be. But then, Descartes argues, it is prudent never wholly to trust in the truth of what we perceive. In ordinary life, of course, we adjust for mistaken perceptions by reference to correct perceptions. But since we cannot be sure at first which cases are veridical and which are not, it is possible (if not always feasible) to doubt any particular bit of apparent sensory knowledge.

  2. The Dream Problem

    Second, Descartes raised a more systematic method for doubting the legitimacy of all sensory perception. Since my most vivid dreams are internally indistinguishible from waking experience, he argued, it is possible that everything I now "perceive" to be part of the physical world outside me is in fact nothing more than a fanciful fabrication of my own imagination. On this supposition, it is possible to doubt that any physical thing really exists, that there is an external world at all. (Med. I)

    Severe as it is, this level of doubt is not utterly comprehensive, since the truths of mathematics and the content of simple natures remain unaffected. Even if there is no material world (and thus, even in my dreams) two plus three makes five and red looks red to me. In order to doubt the veracity of such fundamental beliefs, I must extend the method of doubting even more hyperbolically.

  3. A Deceiving God

    Finally, then, Descartes raises even more comprehensive doubts by inviting us to consider a radical hypothesis derived from one of our most treasured traditional beliefs. What if (as religion teaches) there is an omnipotent god, but that deity devotes its full attention to deceiving me? (Med. I) The problem here is not merely that I might be forced by god to believe what something which is in fact false. Descartes means to raise the far more devastating possibility that whenever I believe anything, even if it has always been true up until now, a truly omnipotent deceiver could at that very moment choose to change the world so as to render my belief false. On this supposition, it seems possible to doubt the truth of absolutely anything I might come to believe.

    Although the hypothesis of a deceiving god best serves the logical structure of the Meditations as a whole, Descartes offered two alternative versions of the hypothetical doubt for the benefit of those who might take offense at even a counter-factual suggestion of impiety. It may seem more palatable to the devout to consider the possibility that I systematically deceive myself or that there is some evil demon who perpetually tortures me with my own error. The point in each case is that it is possible for every belief I entertain to be false.

Remember that the point of the entire exercise is to out-do the skeptics at their own game, to raise the broadest possible grounds for doubt, so that whatever we come to believe in the face of such challenges will indeed be that which cannot be doubted. It is worthwhile to pause here, wallowing in the depths of Cartesian doubt at the end of the First Meditation, the better to appreciate the escape he offers at the outset of Meditation Two.

I Am, I Exist

The Second Meditation begins with a review of the First. Remember that I am committed to suspending judgment with respect to anything about which I can conceive any doubt, and my doubts are extensive. I mistrust every report of my senses, I regard the material world as nothing more than a dream, and I suppose that an omnipotent god renders false each proposition that I am even inclined to believe. Since everything therefore seems to be dubitable, does it follow that I can be certain of nothing at all?

It does not. Descartes claimed that one thing emerges as true even under the strict conditions imposed by the otherwise universal doubt: "I am, I exist" is necessarily true whenever the thought occurs to me. (Med. II) This truth neither derives from sensory information nor depends upon the reality of an external world, and I would have to exist even if I were systematically deceived. For even an omnipotent god could not cause it to be true, at one and the same time, both that I am deceived and that I do not exist. If I am deceived, then at least I am.

Although Descartes's reasoning here is best known in the Latin translation of its expression in the Discourse, "cogito, ergo sum" ("I think, therefore I am"), it is not merely an inference from the activity of thinking to the existence of an agent which performs that activity. It is intended rather as an intuition of one's own reality, an expression of the indubitability of first-person experience, the logical self-certification of self-conscious awareness in any form.

Skepticism is thereby defeated, according to Descartes. No matter how many skeptical challenges are raised—indeed, even if things are much worse than the most extravagant skeptic ever claimed—there is at least one fragment of genuine human knowledge: my perfect certainty of my own existence. From this starting-point, Descartes supposed, it is possible to achieve indubitable knowledge of many other propositions as well.

I Am a Thinking Thing

An initial consequence may be drawn directly from the intuitive certainty of the cogito itself. If I know that I am, Descartes argued, I must also know what I am; an understanding of my true nature must be contained implicitly in the content of my awareness.

What then, is this "I" that doubts, that may be deceived, that thinks? Since I became certain of my existence while entertaining serious doubts about sensory information and the existence of a material world, none of the apparent features of my human body can have been crucial for my understanding of myself. But all that is left is my thought itself, so Descartes concluded that "sum res cogitans" ("I am a thing that thinks"). (Med. II) In Descartes's terms, I am a substance whose inseparable attribute (or entire essence) is thought, with all its modes: doubting, willing, conceiving, believing, etc. What I really am is a mind [Lat. mens] or soul [Lat. anima]. So completely am I identified with my conscious awareness, Descartes claimed, that if I were to stop thinking altogether, it would follow that I no longer existed at all. At this point, nothing else about human nature can be determined with such perfect certainty.

In ordinary life, my experience of bodies may appear to be more vivid than self-consciousness, but Descartes argued that sensory appearances actually provide no reliable knowledge of the external world. If I hold a piece of beeswax while approaching the fire, all of the qualities it presents to my senses change dramatically while the wax itself remains. (Med. II) It follows that the impressions of sense are unreliable guides even to the nature of bodies. (Notice here that the identity of the piece of wax depends solely upon its spatial location; that's a significant hint about Descartes's view of the true nature of material things, which we'll see in more detail in Meditation Five.)

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