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.
Part six of the Discourse is essentially a long-winded explanation as to why Descartes has chosen to publish three scientific essays rather than the massive work that he claims to have compiled. He delicately steps around the main reason, which is the fear aroused in him after Galileo was condemned by the Inquisition. His fears of arousing controversy are not unfounded: in the 1640s, with the publication of the Meditations and the Principles of Philosophy, Descartes indeed found himself caught up in all sorts of academic disputes.
What we find here is a tension between an old world with a worldview of privacy and religious dogma and a new world with a worldview of open scientific inquiry. Descartes's desire to keep his work private is only partly a matter of fear of offending the religious authorities. He is also partly living in a world where knowledge is a highly-prized commodity that should not be shared. Before the printing press (invented some hundred years earlier) books were extremely rare and difficult to come by, so there was a great deal more care in securing the matter contained in them. This is the worldview that led Leonardo da Vinci to write his notebooks in code. In making his findings public, Descartes would be surrendering a prized possession to anyone who could afford it.
On the other hand, Descartes is living in a world of the printing press and of free scientific inquiry, where knowledge is seen as a collective enterprise. This is a world where personal interests take a back seat to the unfolding drama of objective science. This, in theory, is how the modern university system is supposed to work: individual scholars labor away and then make their findings public so that other scholars can learn from them and build upon their work. Descartes also shows clear signs of being a part of this world. Though he is afraid to publish all his principles, he does publish scientific essays with the explicit hope that others will take his lead and build upon his discoveries. It is also significant that he writes in French, and not the Latin of the church and the schoolmen. Descartes is not writing for a scholarly audience, but for the public at large.
Descartes also suggests that he would be content to publish objections to his essays along with his own replies. This practice was never taken up with respect to the Discourse or its appended essays, but the Meditations famously has a lengthy set of objections and replies that are an excellent source, even today, for gaining a clearer understanding of Descartes's ideas. The method of objections and replies, of course, is very much in the spirit of the new age of open scientific inquiry.
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 (see the section on Part Two). 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.