During his lifetime, Rene Descartes was known throughout Europe as a leading contemporary scientist. He developed one of the most plausible versions of the new mechanistic, mathematical accounts of the world and used it to provide thorough explanations in the fields of optics, cosmology, physics, physiology, and biology. Within only a few decades of his death, Descartes' scientific system was all but forgotten, eclipsed by the far superior mechanistic, mathematical science proposed by Sir Isaac Newton. Yet, despite the quick downfall of his scientific system, Descartes remains one of the most widely read thinkers of any age. It is not his science that makes up his legacy, but rather the philosophy that he developed to serve as its foundation.
In seeking a firm philosophical basis on which to rest his scientific theories, Descartes succeeded in developing the first coherent sketch of a recognizably modern philosophical outlook. Until then, all of Western philosophy was simply an attempt to work out minor problems in Aristotle's theories. This Scholasticism, as it was called, had dominated the universities for as long as there had been universities to dominate. To do philosophy, for almost 2000 years, had meant to be a Scholastic philosopher, tinkering with ancient theories.
Descartes was among the first to rebel against this status quo. He saw nothing to commend the Scholastic way of thought, with its reliance on the rules of dialectical argument and its preoccupation with incoherent metaphysical and logical subtleties. Rather than lead its students closer to truth, he felt, it merely confused and misled them. The way to do philosophy, he was certain, was simply to follow one's own inborn faculty of reason. Starting from the simplest and most evident truths, Descartes sought to deduce all of knowledge from basic and indubitable principles. Following this method, he arrived at a conception of the world, of our minds, and of the relation between the two, that catapulted philosophy into the modern age. He initiated a new method for seeking philosophical explanation and provided a host of new philosophical concerns on which to test that method.
The Principles of Philosophy is unique among Descartes' works because it not only offers a comprehensive account of his revolutionary philosophy, but also demonstrates in detail how this philosophy serves as a foundation for his science. Descartes' other writings focus either on his philosophy or on his science; it is only the Principles that explicitly demonstrates how intimately related these two aspects of his thought really are, by presenting them in their entirety. The work, therefore, gives us a chance to see both what the first modern philosophical system looked like, and why it was developed in the first place. Ironically, though the metaphysical and epistemological claims of the book were originally intended to support the scientific claims, today the scientific claims are only read in order to help us better understand Descartes' groundbreaking metaphysics and epistemology.