Rene Descartes is frequently considered the first modern philosopher. His first publication, Discourse on Method (1637), was the touchstone of the scientific method. A response to the lack of clarity he saw in the world of science, Discourse describes how scientific study should be prosecuted so as to achieve the utmost clarity, by using deductive reasoning to test hypotheses. Descartes explained that the test of an alleged truth is the clarity with which it may be apprehended, or proven. "I think, therefore I am," (cogito ergo sum) is Descartes' famous example of the most clearly apprehended truth. In effect, the evidence of thought proves the hypothesis of existence.
Descartes dabbled extensively in the study of cosmology and the nature of matter, developing theories on the make up of matter and the formulation and operation of heavenly bodies. Though Descartes' astronomical explanation failed to account for many observed phenomena, his great prestige propelled his theory into fashion among the educated elite intellectuals of Europe. Descartes was even about to publish a book on cosmology, entitled The World, in 1653, when he heard of Galileo Galilei's condemnation by the Church and thought better of it. Descartes tried to apply his physical theories and expand upon them in his works on human anatomy, which, though pioneering in some respects, were largely erroneous. He further wrote about the spiritual nature of man and theorized about the existence of the soul. The Cartesian philosophy (derived from his name, Descartes) won many followers during the seventeenth century.
Francis Bacon, also called Lord Verulam, was somewhat less renowned and less successful than Descartes, but nevertheless highly influential. Bacon advocated the collection of all possible facts and phenomena and the processing of these through a sort of automatic logical mill. Bacon warned scientists against four famous false notions, called Idols.
1. Idols of the Tribe were fallacies in humankind, most notably man's proneness to believe that nature was ordered to a higher degree than it actually was.
2. Idols of the Cave were misconceptions inherent in individuals' thoughts, spawned by private prejudices.
3. Idols of the Marketplace were errors that arose from received systems of thought.
4. Idols of the Theatre were errors spawned by the influence of mere words over the human mind.
This set of theories received varying levels of acceptance and rejection, and ultimately left only a limited impact on the world of science. However, Bacon did make great and lasting strides in advocating a more logical scientific community less prone to reliance on authority and mysticism. Bacon's most well known work, Novum Organum (1620), attempts to provide for the organization of the scientific community by the manner in which the various fields of science relate to each other. His theories on logic and the organization of the sciences had a great effect on science in his time and into the future.
The scientific method of the Middle Ages had revolved around Aristotle's inductive method of reasoning, in which a scientist gathers facts about individual cases and uses them to reach a conclusion or theory. Descartes' great contribution was the introduction of deductive reasoning, in which the scientist first formulates an educated hypothesis, and then seeks evidence to support or disprove that hypothesis. The deductive method did not replace the inductive method, but it added to the tools of scientists of the era, and proved useful on many occasions.
Though Descartes the philosopher advocated order and rationality in method, Descartes the scientist did not always adhere to his own philosophy. Had he been as critical of his own theories as he was of those of others, including Galileo's, he would surely have seen that his theories on the make up of the cosmos, which revolved around a system of major and minor vortices, were clearly disproved by recorded observations. Further, his proposed anatomical theories, while complex and interesting, were untenable as the explanations for real phenomena.
Despite his shortcomings as a scientist, Descartes made many valuable contributions to science, mathematics, and most of all, philosophy. The Cartesian philosophy was the first complete and coherent philosophical system of modern times. It quickly attracted a following, and even was adopted by the clergy in many cases. Gradually, however, science exposed the errors in Descartes' scientific claims, and his following dwindled. However, Descartes had laid the foundation of modern philosophy, and left behind him a long chain of thinkers who believed that truth could be reached with the power of the human mind.
While Bacon was well respected in his time, it was not long before others began to poke holes in his philosophy, citing elements which were left out, and the lack of applicability in many cases. Yet despite Bacon's faults as a philosopher and failures as a scientist, the world owes him a great debt. Bacon observed the vices and misconceptions clung to by the scholastics of his time, and advocated the focus on ethics and logic, free from the restricting influence of the Church and many of the accepted ancient thinkers. He clearly and vigorously denounced the misconceptions and errors that had held scientific progress back during the Middle Ages, and thus expressed the spirit of the Scientific Revolution. His ideas on the cooperation and interaction of the fields of science factored greatly into the later establishment of the Royal Society in London and similar societies elsewhere, where scientists from different fields collaborated to advance science and technology as a whole. His thoughts on ethics were an inspiration to Enlightenment thinkers, who continued to advocate the practical application of Bacon's ethical code. Whatever his failings, Bacon succeeded in rousing the enthusiasm and spirit of logical inquiry of the scientists of his day and beyond. It is a further measure of respect to Bacon that a few of literary scholars, unbelieving that a mere commoner could have written Shakespeare's great plays, have attributed the works of Shakespeare to Bacon.