Discourse on the Method

Descartes begins by allowing himself some wit:

Good sense is, of all things among men, the most equally distributed; for every one thinks himself so abundantly provided with it, that those even who are the most difficult to satisfy in everything else, do not usually desire a larger measure of this quality than they already possess.

"...the reading of good books is like a conversation with the best men of past centuries–" (Discourse part I, AT p. 5)

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,"[3] 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."[4][5] Descartes continues with a warning:[6]

For to be possessed of a vigorous mind is not enough; the prime requisite is rightly to apply it. The greatest minds, as they are capable of the highest excellences, are open likewise to the greatest aberrations; and those who travel very slowly may yet make far greater progress, provided they keep always to the straight road, than those who, while they run, forsake it.

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."

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, or 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 lay within the compass of his powers; he presents four precepts:[7]

The first was never to accept anything for true which I did not clearly know to be such; that is to say, carefully to avoid precipitancy and prejudice, and to comprise nothing more in my judgment than what was presented to my mind so clearly and distinctly as to exclude all ground of doubt.

The second, to divide each of the difficulties under examination into as many parts as possible, and as might be necessary for its adequate solution.

The third, to conduct my thoughts in such order that, by commencing with objects the simplest and easiest to know, I might ascend by little and little, and, as it were, step by step, to the knowledge of the more complex; assigning in thought a certain order even to those objects which in their own nature do not stand in a relation of antecedence and sequence.

And the last, in every case to make enumerations so complete, and reviews so general, that I might be assured that nothing was omitted.

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. The following three maxims were adopted by Descartes so that he could effectively function in the "real world" while experimenting with his method of radical doubt. They formed a rudimentary belief system from which to act before he developed a new system based on the truths he discovered using his method:

1. The first was to obey the laws and customs of my country, adhering firmly to the faith in which, by the grace of God, I had been educated from my childhood and regulating my conduct in every other matter according to the most moderate opinions, and the farthest removed from extremes, which should happen to be adopted in practice with general consent of the most judicious of those among whom I might be living.
2. Be as firm and resolute in my actions as I was able.
3. Endeavor always to conquer myself rather than fortune, and change my desires rather than the order of the world, and in general, accustom myself to the persuasion that, except our own thoughts, there is nothing absolutely in our power; so that when we have done our best in things external to us, our ill-success cannot possibly be failure on our part.

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.

Here he describes how in other writings he discusses the idea of laws of nature, of the sun and stars, the idea of the moon being the cause of ebb and flow, on gravitation, and going on to discuss light and fire.

Describing his work on light, he states:

[I] expounded at considerable length what the nature of that light must be which is found in the sun and the stars, and how thence in an instant of time it traverses the immense spaces of the heavens.

His work on such physico-mechanical laws is, however, projected into a "new world." A theoretical place God created

somewhere in the imaginary spaces [with] matter sufficient to compose ... [a "new world" in which He] ... agitate[d] variously and confusedly the different parts of this matter, so that there resulted a chaos as disordered as the poets ever feigned, and after that did nothing more than lend his ordinary concurrence to nature, and allow her to act in accordance with the laws which he had established.

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".

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.[8]^: 51 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.[9] 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, which are identified as our faculty for rational thinking. Hence the term "I think, therefore I am." All three of these words (particularly "mind" and "soul") can be identified by the single French term âme.

Descartes begins by noting, without directly referring to it, the recent trial of Galileo for heresy and the condemnation of heliocentrism; he explains that for these reasons he has been slow to publish.[10]

I remarked, moreover, with respect to experiments, that they become always more necessary the more one is advanced in knowledge; for, at the commencement, it is better to make use only of what is spontaneously presented to our senses. First, I have essayed to find in general the principles, or first causes of all that is or can be in the world.

Secure on these foundation stones, Descartes shows the practical application of "the Method" in Mathematics and the Science.