 |
|
Plate
15 from Nova Reperta |
 |
|
Descartes's
Body-Machine |
|
|
René Descartes is best known for having introduced a metaphysical dualism, arguing that mind and matter are two distinct and separable substances. As a result, he is often blamed for various ills of the modern world, most notably the alienation of mind from body, individual from world, and thought from action. Descartes developed his metaphysics in response to competing demands that arose from the lack of clear boundaries between theology, philosophy and science. He aimed to displace the entrenched Aristotelian philosophy of the schools with his vision of a new mathematical science that would explain all natural phenomena by means of a few universal laws of nature. Since what we now call "science" formed part of natural philosophy in his period, Descartes's new science required a philosophical justification. Nor were the questions of natural philosophy clearly separated from theology. Thus Descartes also had to ensure that his new natural philosophy preserved the Christian ideals of free will and the afterlife. Prior to Descartes, Aristotle's metaphysics, and the account of the soul that it entailed, had prevailed in Western Europe. Aristotle (384-322 BC) accounted for the distinct character of each individual thing in terms of its matter and form. Matter is the material out of which a thing is made, e.g., the iron of an axe or the flesh and bones of a person. But matter always has to have a form, an organizing principle that makes it one kind of material rather than another. The iron of an axe has to have the form of iron before it can become the material for the axe, for if it had the form of rubber, it would not be capable of taking on the form of an axe (although it would be suited to become a tire). Flesh and bones likewise have distinct forms. The yielding nature of flesh is due to its form, and this makes it capable of constituting different organs. By contrast the form of bone makes it unyielding and thus suited for the skeleton. In nature, as in art, everything in Aristotle's universe has a distinct structure and purpose. Matter without any shape, size, texture, structure, color, temperature—in short, matter without any form at all—simply could not exist. Therefore, even if we break a thing down to its most basic elements (for Aristotle, earth, air, fire, and water) they will still be a combination of matter and form. Thus matter, for Aristotle and his followers, is defined relative to form. It is, in effect, the capacity to take on form. At each level of complexity, we find materials with certain forms, making them capable of taking on some additional forms, but not others. Thus flesh and bones can acquire the form of an organism, but iron cannot. Aristotle calls the form that makes a body a living body the soul (psyche). As a form, the soul is nothing more than the actualization of the potentials of the matter it informs, and is inseparable from the mortal body. The form of a living thing is identical to its life functions, which for plants includes nutritive and reproductive functions (the nutritive soul), for animals, the latter plus locomotive and sensitive functions (the sensitive soul), and for humans, in addition to all of the above, the intellective functions (the intellective soul). The intellective soul is the only one that is not dependent on the body for some of its actions. Christian medieval philosophers, like St. Thomas Aquinas (1224-1274), accepted Aristotle's definition of the soul but sought to reconcile it with the Christian belief in the immorality of the soul. Since personal immortality requires that individual souls (and their memories) be separable from their bodies, adjustments had to be made to Aristotle's conception of the soul to show that it could survive the body. In constructing a philosophical foundation for his new science, Descartes rejected Aristotle's metaphysics. Instead of defining matter relative to form, he defined matter as a distinct, passive substance, possessing only the geometrical attributes of extension, i.e., size, shape, number, and motion. Certain forms are built into matter, as it were, and matter can only take on variations of these basic forms, i.e., the parts of material substance can take on particular sizes, shapes, numbers and motions (what Descartes calls modes of matter) but not colors, sounds, temperatures, etc. This view accounts well for the relations between inanimate bits of matter, but Descartes was hard pressed to explain how particles, possessing only these modes, could give rise to a living body that not only breathes, digests, and reproduces, but sees colors, hears sounds, remembers, responds emotionally, and engages in abstract thinking. For Aristotelian philosophers, all the latter functions, except pure intellectual thought, are realizations of potentials inherent to the living human body. But Descartes's geometrical conception of matter did not allow for such a complex view of the body. Descartes addresses this problem in the Meditations on First Philosophy by creating a division between mind and body. For example, in Meditation Six he explains the causes of bodily sensations—such as pain, pleasure, thirst, and hunger—in terms of the motions of material particles and the mechanisms by which these motions are transmitted via the nerves to the brain. But the sensations themselves are located in a separate substance—the thinking thing—which Descartes describes as that which senses, imagines, remembers, doubts, thinks abstractly, and wills freely. By making the mind and body two distinct and separable substances, Descartes was able to redefine matter so that all its properties could be described mathematically while preserving personal immortality and freedom of the will for the human soul. However, it was not clear how these two distinct substances could form one unified human being and interact with each other through the pineal gland in the brain. The Treatise on Man, published posthumously, is Descartes's main work involving traditional Aristotelian themes. There, Descartes seems to focus more on the relationship between the physical and the mental. He gives, for instance, an account of the physiological processes involved in perception and memory. At the beginning of this work, Descartes invites us to imagine the human body as "an earthen machine" (or an automaton) and implies that though more complex, the movements of this machine can be explained in the same way as the movements of clocks, fountains, or mills. This is a radically new conception of a living body and yet, as John Sutton argues in Philosophy and Memory Traces, when it comes to giving specific explanations, Descartes retains several traditional principles. For example, Descartes's conception of bodily functions in terms of a kind of fluid dynamics is reminiscent of ancient and medieval humoral theories that attributed the health and proper functioning of the body to a balance among four basic bodily fluids (humors). Descartes's animal spirits, like those posited by the ancient physician Galen (129/30-199/200), are concocted from blood and responsible for moving muscles and communicating motions to the seat of perception in the brain. While physical, these animal spirits seem to play the role of intermediary between mind and body. A diagram, which appears
in Part I of the A pair of images found
in Part V of the French edition represent cross sections of the
brain, and While it is clear that Descartes drew on ancient and medieval theories to flesh out the details of his account of bodily processes, his novel conception of the body as a machine that performs basic functions independently of the soul paved the way for more recent attempts to reduce higher cognitive functions to physiological changes in the brain. Helen Hattab Suggested Reading
|
