The modern emphasis on the individual further strengthened the rejection of tradition as a source of truth. It was common for pre-modern scientists to support their arguments by appealing to Aristotle or some Church Father or earlier writer. Descartes and his 17th century contemporaries rejected all this, claiming that much of this past work was deeply flawed. From now on, the only true authority in matters of science was to be one’s own reason and nature itself. By the next century, this attitude had spread to the moral and political realms as well:
Enlightenment is man’s exit from his self-incurred immaturity. Immaturity is the inability to make use of one’s own understanding without the guidance of another. This inability is self-incurred if its cause lies not in the lack of understanding, but rather in the lack of resolution and courage to use it without the guidance of another. Sapere aude! Have the courage to use your own understanding! is the motto of the enlightenment.
So began Immanuel Kant’s (1724-1804) famous essay on enlightenment published in 1784. It continues:
Laziness and cowardice are the causes why such a great part of mankind, long after nature has set them free from the guidance of others, still gladly remain immature for life and why it is so easy for others to set themselves up as guardians. It is so comfortable to be immature. If I have a book that understands for me, a pastor who has a conscience for me, a doctor who decides my diet for me, etc., I do not need to trouble myself at all. I have no need to think, if only I can pay; others will take over the tedious business for me.
For René Descartes (1596-1650), the immediate task of the natural sciences was clear: we must rebuild everything from the ground up. What is more, he felt that he could do this single-handedly, indeed, that any “man of good sense” could rebuild the sciences by himself, without recourse to tradition and past authorities like Aristotle. Descartes tells us of his realization that what science needed was a new method:
I was in Germany then, where the wars — which are still continuing there — called me; and while I was returning to the army from the coronation of the emperor, the onset of winter held me up in quarters where, finding no conversation with which to be diverted and, fortunately, otherwise having no worries or passions which troubled me, I remained for a whole day by myself in a small stove-heated room, where I had complete leisure for communing with my thoughts. Among them, one of the first that I thought of considering was that often there is less perfection in works made of several pieces and in works made by the hands of several masters than in those works on which but one master has worked. Thus one sees that buildings undertaken and completed by a single architect are commonly more beautiful and better ordered than those that several architects have tried to patch up, using old walls that had been built for other purposes. Thus these ancient cities that were once merely straggling villages and have become in the course of time great cities are commonly quite poorly laid out, compared to those well-ordered towns that an engineer lays out on a vacant plain as it suits his fancy.
In this metaphor of a town, Descartes is describing the shabby state of the natural sciences as he found them in the early 17th century. Aristotle had argued that each discipline — biology, meteorology, astronomy, etc. — should have its own distinct method or approach of pursuing its science. This resulted, Descartes felt, in a hodge-podge of science, lacking in both certainty and in order, and that the whole mess should be torn down and started anew:
And thus I thought that book learning, at least the kind whose arguments are merely probable and have no demonstrations — having been built up from and enlarged gradually by the opinions of many different people — does not draw as near to the truth as the simple reasonings that can be made naturally by a man of good sense concerning what he encounters. [Descartes, Discourse on Method (1637), translated from the French by Donald Cress]