The Discourse on the Method is a fascinating book, both as a work of philosophy and as a historical document. Descartes lived and worked in a period that Thomas Kuhn would call a "paradigm shift": one way of thinking, one worldview, was slowly being replaced by another. Descartes's work, while part of the new paradigm, still has one leg in the old mode of thought.
The old, waning worldview was scholastic Aristotelianism. The Aristotelian paradigm had a conception of the mind, of knowledge, and of science that may seem very alien to us today, but this conception held sway over Western thought for about two thousand years.
According to the Aristotelian tradition, the mind proper—what is exclusively "inside the head"—is limited to reason and understanding. Sensory perception, imagination, will, and so on, make reference to things outside the mind and so are not purely mental. Rather, they are the link that connects us to the outside world. According to Aristotle, there is no distinction between what I perceive and what is "out there." Thus, sensory experience gives us direct and immediate knowledge of objects in the world.
Science, in this worldview, is a matter of taking the immediate evidence of sensory experience and deducing certain conclusions from it. The sensory experience is indubitable, and the deductions are logical, so all scientific knowledge is based on absolute certainty.
One of Descartes's most significant contributions to the scientific revolution is his conception of sensory experience, imagination, and will as being just as much subjective mental phenomena as reason and understanding. His systematic doubting questions how it is that we can be certain about what we perceive. Descartes draws a sharp distinction between what our senses report to us and what is "out there."
This re-conception of the mind shakes the foundations of Aristotelian scholasticism. If sensory experience is no longer self-evident, then we can no longer deduce certain scientific truths from these observations. Essentially, Descartes makes us sharply aware of what goes into a scientific observation. It is not a purely neutral and objective act of seeing the world as it is; it is an interpretive act that must be undertaken with great care and circumspection.
The scientific paradigm that we have today owes a great deal to Descartes. Today, we have taken Descartes's method one step further. Now, we conclude that we can never have absolute certainty in the sciences. All we can hope for are sound theories that are supported by careful observations.
Descartes himself does not reach this conclusion. To a large extent, he is still set on finding certainty. His search for certainty, beginning with the famous line "I am thinking, therefore I exist," has largely defined the course of a great deal of philosophy since his time. We can debate whether Descartes is right in having found certainty in this claim, and we can debate what kind of knowledge this is, but it seems clear that it is not a kind of knowledge that is applicable to science as a whole. In finding this certainty, Descartes hopes to rebuild science in the Aristotelian method of deduction from certain first principles. In hindsight, this effort may seem a bit misguided.
Though his philosophy of science may be a bit askew, the philosophical method Descartes uses in part four of the Discourse has proven extremely valuable. His method of skeptical doubt has raised important philosophical questions concerning how we can be certain of, or even know, anything at all. His re-conception of what the mind is has largely defined the shape of Western psychology and philosophy ever since. His assertion that he is essentially a thinking thing and that his mind is distinct from his body has also raised a number of important philosophical questions: what is my relationship with my mind? What is my relationship with my body? If they are distinct, what is the causal connection between the two? And so on. Effectively, Descartes frames the questions that have preoccupied what we now call "modern philosophy."
The turning point in Descartes's intellectual development occurred on November 10, 1619. He had attended the coronation of Ferdinand II in Frankfurt, and was returning to serve in the army of Maximilian of Bavaria. Due to the onset of winter, he holed himself up for a day, alone in a stove-heated room. With nothing else to occupy him, he set about thinking.
He first mused that accomplishments of single individuals are usually more perfect than group efforts. Cities and buildings are more beautiful when they are made according to a single plan than when they are patched together piecemeal. Similarly, laws are better when they come from a single mind than when they evolve gradually over time. Descartes cites God's law as an instance of this perfection. These musings suggest to him that a person is best served by following the guidance of his reason alone, and not letting his judgments be clouded by his appetites and by the opinions of others.
While it would be impossible to resolve the imperfections of a state or a body of sciences by tearing it all down and starting again from scratch, Descartes suggests that such a method is not quite as unreasonable on the individual level. He decided to let go of all his former opinions at once, and re-build them anew according the exacting standards of his own reason.
Descartes is very careful, first of all, to point out that this method is meant only on an individual level, and he strongly opposes those who would try to topple a public institution and rebuild it from the ground up. Second, he reminds us that he only wants to discuss his method with us; he is not telling us to imitate him. In particular, he notes that there are two types of people for whom this method would be unsuited: those who think they know more than they do and who lack the patience for such careful work, and those who are modest enough to think that they are more capable of finding out the truth if they follow a teacher. Descartes would count himself among this second group if he hadn't had such a number of teachers and embarked on so many travels as to realize that the opinions of even learned men vary greatly.
Before abandoning his former opinions entirely, Descartes formulates four laws that will direct his inquiry: First, not to accept anything as true unless it is evident; this will prevent hasty conclusions. Second, to divide any given problem into the greatest possible number of parts to make for a simpler analysis. Third, to start with the simplest of objects and to slowly progress toward increasingly difficult objects of study. Fourth, to be circumspect and constantly review the progress made in order to be sure that nothing has been left out.
An obvious starting place was in the mathematical sciences, where a great deal of progress and certain knowledge had been achieved by means of demonstration. Descartes found his work made considerably easier if, on the one hand, he considered every quantity as a line, and, on the other hand, developed a system of symbols that could express these quantities as concisely as possible. Taking the best elements of algebra and geometry, he had tremendous success in both these fields.
Before applying this method to the other sciences, Descartes thought it well to find some philosophical foundations for his method.
If we were to identify a starting point for modern philosophy, November 10, 1619 would be as good a date as any. We might pinpoint precisely the moment that Descartes resolved to cast all his former opinions into doubt. This process of methodological doubt is central to Descartes, and indeed to most of modern philosophy. The results Descartes achieves by employing this method of doubt are discussed in Part Four of theDiscourse, so we will comment on his method in greater detail there.
It is important, of course, that Descartes does not simply scrap everything he knows, or else he would have no guidance in rebuilding his knowledge. The four rules he lays out are meant as guidelines, so that he will be able to rely on them, and not on unnoticed prejudices. Descartes had initially collected twenty-one rules entitled Rules for the Direction of Our Native Intelligence in 1628, but left the manuscript unpublished. The four rules we find here can be read as a major abbreviation of that effort. Essentially, they demand that an inquiry proceed slowly and carefully, starting with basic, simple, self-evident truths, building toward more complex and less evident propositions.
Descartes assumes a certain kind of theory of knowledge that was pretty much unquestioned in his day. In modern philosophical language, we call this a foundationalist epistemology. It sees knowledge as built up from simple, self-evident propositions, to higher and more complex knowledge. The theory states that if we were to analyze any complex proposition, we could break it down into increasingly smaller, simpler pieces until we were left with simple, non-analyzable propositions. These basic propositions would be either self-evidently true or self-evidently false. If they were all true, then we would know that the original complex proposition was also true. Of course, there are different variations of foundationalist epistemology; for example, the epistemology will shift depending on how the analysis is supposed to take place or on what the basic propositions are supposed to look like. But the general idea can be applied to Descartes easily. Knowledge is built up like a skyscraper, with the higher, complex knowledge built on simple, sturdy foundations.
This is just one of a number of theories of knowledge that are batted about these days. Another theory that will come into play later in the Discourse is a coherentist epistemology, one that states that knowledge is more like a circle than a skyscraper. According to this theory, there is no foundational knowledge that is more basic than other knowledge. All knowledge fits together in such a way that it is internally coherent, but there is no fundamental self-evident proposition that is itself beyond doubt and that justifies all the other propositions. A statement is true because it is consistent with everything else we know to be true, not because it can be analyzed into simple parts.
The reason that a foundationalist epistemology seems natural to Descartes at this point is that this is the epistemology that philosophy had inherited from Aristotle. As we have noted already in other sections of this SparkNote, Aristotelian scientific method works according to a system of syllogism and demonstration, where complex truths are logically deduced from simpler ones. This method implies a theory of knowledge according to which complex truths are built upon simpler ones that serve as an unquestioned bedrock of knowledge.
It is significant that Descartes should choose mathematics to study according to this method. Mathematics has had far more success than any other field (except logic) with deductive reasoning. Math is built upon simple, self-evident axioms that are then used, along with some rules of inference, to derive proofs of more complex propositions.
Descartes is not only one of the greatest philosophers of the modern world, he is also one of its greatest mathematicians. His discussion of algebra and geometry alludes to his discovery of analytic geometry that brought those two fields together. Until Descartes, algebra and geometry were two totally separate fields of study. He invented the Cartesian co-ordinate system that every math student knows and loves. That's the co-ordinate system with the x-axis and the y-axis that allows you to plot lines and curves and whatever other shapes you please. Geometrical figures could be plotted onto the co-ordinate grid, and since every line and curve on the grid corresponds to an equation, geometrical figures can be expressed as equations. Geometrical figures become algebraic equations, and algebraic equations can be graphed as geometrical figures. This all seems pretty commonplace to us today, but if you try to imagine solving math problems without graphing anything you'll begin to understand the colossal contribution Descartes made to mathematics.
Descartes claims that he generally feels no inclination to publish his views. However, the success he has had with his method and his principles of physics suggests to him that they could prove an enormous benefit to mankind if made public, particularly when applied in the fields of engineering and medicine. Because he is incapable of fully exploring all these fields by himself, he had hoped that in making his findings public he would enable others to contribute as well. Positing God as the first cause of everything that is, and using his method, it is not difficult to come up with explanations for most straightforward observations. Deducing the many particularities of earthly phenomena, however, requires careful study and observation, and Descartes hopes many specialists will contribute to this cause.
However, he decided not to publish his principles of physics (as expressed in The World) because he fears the controversies they may arouse may distract him from his work. He continues to record carefully all his observations and discoveries, however, and intends to have them published after his death. That way, he may work uninterrupted during his life, and posterity may benefit from his discoveries. All his progress to date has resulted from overcoming only five or six difficulties, and he expects that he may overcome all his remaining difficulties within his lifetime if only he can stay free from controversy.
People might object that by publishing his views Descartes will allow others to identify possible errors in his writings and to develop new directions that Descartes had not thought of. However, Descartes replies, he has yet to hear a plausible objection that he has not himself already anticipated. Further, he does not feel he has taken his investigations far enough that others can develop new directions from it. Even the people with the best minds—people who are capable of philosophical speculation—may not benefit from his work as it stands. If they prefer to appear knowledgeable rather than confessing their ignorance and working toward the truth, they will not want to follow his method. And if they do hope to gain knowledge for themselves, they won't want to use his findings but pursue their own investigations. Help can often be a nuisance and a hindrance, and Descartes is happier working alone and free from controversy.
For these and other reasons, Descartes decided three years ago not to publish the principles of his physics. However, he has come to publish this work, along with the appended essays (see the Context file) for two reasons. One is to dispel any rumors that his discoveries are false, and the other is because he feels he needs the help of other scientists if his work in certain fields is to advance. He hopes that people will examine his essays in optics, meteorology, and geometry, and he promises to publish any worthwhile objections to these essays, along with his replies, in a future edition of the work.
Descartes remarks that the "suppositions" that serve as first principles in his essays are not argued for, but he feels that they are made evident by the results that follow from them, just as those results are made evident by the suppositions. He believes these suppositions can be deduced from his first principles, but, for the reasons stated above, he does not wish to make this deduction publicly.
Having explained his reasons for writing in French rather than Latin, Descartes closes by expressing his plans to devote the rest of his life to scientific study without hope for fame or profit.
We should make a final note regarding the "suppositions" that Descartes mentions with respect to the essays that follow. According to Descartes's epistemology, all his claims should follow deductively from the "first principles" contained in his physics. However, he has already claimed that he doesn't want to make these first principles public. The starting point of his scientific essays then, is not these evident first principles themselves, but "suppositions" that he claims he can infer deductively from those first principles. He doesn't give any further reasons to support the truth of his suppositions, but he suggests that they should be confirmed to some degree by the results that follow them.
An example might help clarify this. Newton's second law—that force is equal to mass times acceleration—is not in itself particularly obvious. However, we can apply Newton's second law to a great many everyday phenomena and find that it serves as a very potent explanation for why things work the way they work. We derive a great many results from the "supposition" of Newton's second law, and the familiarity of these results serves to confirm the second law, even though these results themselves are deduced from the second law.
What is interesting about all this is that it could be read as an attempt at defending a coherentist epistemology. While Descartes is ultimately loyal to a foundationalist epistemology, claiming that everything can be derived from his first principles, he is asking his readers to rest content with something else. Neither his suppositions nor the results that he infers from them have the kind of certainty that Descartes claims he can find, but he hopes that the fact that suppositions and results hold together in a clear manner will be evidence enough for the time being.
Ultimately, we have come to see science not as a deduction from first principles, but as a set of theories confirmed by observation. Descartes's insistence on first principles of absolute certainty is, in a sense, a holdover from an earlier age.
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