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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.