The book is divided into six parts, described in the author's preface as: • Various considerations touching the Sciences • The principal rules of the Method which the Author has discovered • Certain of the rules of Morals which he has deduced from this Method • The reasonings by which he establishes the existence of God and of the Human Soul • The order of the Physical questions which he has investigated, and, in particular, the explication of the motion of the heart and of some other difficulties pertaining to Medicine, as also the difference between the soul of man and that of the brutes • What the Author believes to be required in order to greater advancement in the investigation of Nature than has yet been made, with the reasons that have induced him to write
Part I: Various scientific considerations Descartes begins by allowing himself some wit: A similar observation can be found in Hobbes, when he writes about human abilities, specifically wisdom and "their own wit": "But this proveth rather that men are in that point equal, than unequal. For there is not ordinarily a greater sign of the equal distribution of anything than that every man is contented with his share," but also in Montaigne, whose formulation indicates that it was a commonplace at the time: "Tis commonly said that the justest portion Nature has given us of her favors is that of sense; for there is no one who is not contented with his share." Descartes continues with a warning: Descartes describes his disappointment with his education: "[A]s soon as I had finished the entire course of study…I found myself involved in so many doubts and errors, that I was convinced I had advanced no farther…than the discovery at every turn of my own ignorance." He notes his special delight with mathematics, and contrasts its strong foundations to "the disquisitions of the ancient moralists [which are] towering and magnificent palaces with no better foundation than sand and mud."
Part II: Principal rules of the Method Descartes was in Germany, attracted thither by the
wars in that country, and describes his intent by a "building metaphor" (see also:
Neurath's boat). He observes that buildings, cities or nations that have been planned by a single hand are more elegant and commodious than those that have grown organically. He resolves not to build on old foundations, nor to lean upon principles which he had taken on faith in his youth. Descartes seeks to ascertain the true method by which to arrive at the knowledge of whatever lies within the compass of his powers. He presents four precepts:
Part III: Morals and Maxims of conducting the Method Descartes uses the analogy of rebuilding a house from secure foundations, and extends the analogy to the idea of needing a temporary abode while his own house is being rebuilt. Descartes adopts the following "three or four" maxims in order to remain effective in the "real world" while experimenting with his method of radical doubt. They form a rudimentary belief system from which to act before his new system is fully developed: Finally, Descartes states his resolute belief that there is no better use of his time than to cultivate his reason and to advance his knowledge of the truth according to his method.
Part IV: Proof of God and the Soul Applying the method to itself,
Descartes challenges his own reasoning and
reason itself. But Descartes believes three things are not susceptible to doubt and the three support each other to form a stable foundation for the method. He cannot doubt that something has to be there to do the doubting:
I think, therefore I am. The method of doubt cannot doubt reason as it is based on reason itself. By reason there exists a God, and God is the guarantor that reason is not misguided. Descartes supplies three different proofs for the existence of God, including what is now referred to as the
ontological proof of the existence of God.
Part V: Physics, the heart, and the soul of man and animals Descartes briefly sketches how in an unpublished treatise (published posthumously as
Le Monde) he had laid out his ideas regarding the laws of nature, the sun and stars, the moon as the cause of "ebb and flow" (meaning the
tides), gravitation, light, and heat. Describing his work on light, he states: His work on such physico-mechanical laws is, however, framed as applying not to our world but to a theoretical "new world" created by God Descartes does this "to express my judgment regarding ... [his subjects] with greater freedom, without being necessitated to adopt or refute the opinions of the learned." (Descartes' hypothetical world would be a
deistic universe.) He goes on to say that he "was not, however, disposed, from these circumstances, to conclude that this world had been created in the manner I described; for it is much more likely that God made it at the first such as it was to be." Despite this admission, it seems that Descartes' project for understanding the world was that of re-creating creation—a cosmological project which aimed, through Descartes' particular brand of experimental method, to show not merely the possibility of such a system, but to suggest that this way of looking at the world—one with (as Descartes saw it) no assumptions about God or nature—provided the only basis upon which he could see knowledge progressing (as he states in Book II). Thus, in Descartes' work, we can see some of the fundamental assumptions of modern cosmology in evidence—the project of examining the historical construction of the universe through a set of quantitative laws describing interactions which would allow the ordered present to be constructed from a chaotic past. He goes on to the motion of the blood in the heart and arteries, endorsing the findings of "a physician of England" about the circulation of blood, referring to
William Harvey and his work
De motu cordis in a marginal note. But then he disagrees strongly about the function of the heart as a pump, ascribing the motive power of the circulation to heat rather than muscular contraction. He describes that these motions seem to be totally independent of what we think, and concludes that our bodies are separate from our
souls. He does not seem to distinguish between
mind,
spirit, and soul, all of which he identifies with our faculty for rational thinking. Hence the term
"I think, therefore I am." All three of these words (particularly "mind" and "soul") can be signified by the single French term
âme.
Part VI: Prerequisites for advancing the investigation of Nature Descartes begins by obliquely referring to the recent trial of
Galileo for heresy and the Church's condemnation of
heliocentrism; he explains that for these reasons he has held back his own treatise from publication. However, he says, because people have begun to hear of his work, he is compelled to publish these small parts of it (that is, the
Discourse,
La Dioptrique, ''
, and La Géométrie) in order that people not
wonder why he doesn't'' publish. The discourse ends with some discussion of scientific experimentation: Descartes believes that experimentation is indispensable, time-consuming, and yet not easily delegated to others. He exhorts the reader to investigate the claims laid out in
Dioptrique,
Météores, and
Géométrie and communicate their findings or criticisms to his publisher; he commits to publishing any such queries he receives along with his answers. ==Influencing future science==