The Unity of Philosophical Experience by Etienne Gilson
This book was recommended to me by a former professor. I had asked him what constitutes a knowledge tradition, and he recommended this book, among others, as a starting place. The book takes the form of a selective history of philosophy beginning with Medieval philosophy and ending with commentary on the state of the art as it looked in 1937 when Gilson wrote the book. The book has four main parts. The first three cover "The Medieval Experiment," "The Cartesian Experiment," and "The Modern Experiment." A concluding chapter ("The Nature and Unity of Philosophical Experience") ties together the themes of the book and explains Gilson's selectivity in his history of philosophy.
There are two main thoughts developed in the book. First, that there is a unique philosophical experience. Second, that there is something that unifies that philosophical experience.
What is philosophical experience? First, it's an experience. (Duh.) Now think of an experience of seeing a red book. It is a perceptual experience, and there is something to the experience that singles it out from all other experiences. What that something is is a matter of debate among philosophers, but that's not of interest to us here. Now think about what it might mean to have a philosophical experience instead of a perceptual experience (or an auditory experience, or gastronomic experience, or religious experience, etc.). What sorts of things are going to be involved in a philosophical experience? In the perceptual experience, things like color and shape and vision are parts of the experience, and we would say that the central part of the perceptual experience is that you experience the seeing of something. What brings together all the parts of that experience into one experience is your seeing the red book.
But now what is the unity of philosophical experience? Gilson says that it is Being. It is Being because only Being can be the "cause" of the laws (or, to put it another way, justify the conclusions) that can be inferred from Gilson's survey of philosophical experience. There are a number of these laws or conclusions. I'll just quote from Gilson (his words are in blue).
Philosophy always buries its undertakers.
By his very nature, man is a metaphysical animal.
Metaphysics is the knowledge gathered by a naturally transcendent reason in its search for the first principles, or first causes, of what is given in sensible experience.
As metaphysics aims at transcending all particular knowledge, no particular science is competent either to solve metaphysical problems, or to judge their metaphysical solutions.
The failures of the metaphysicians flow from their unguarded use of a principle of unity present in the human mind.
Since being is the first principle of all human knowledge, it is a fortiori the first principle of metaphysics.
All the failures of metaphysics should be traced to the fact, that the first principle of human knowledge has been either overlooked or misused by the metaphysicians.
Since philosophical experience is an experience, it cannot be adequately captured in words (just like I could not really capture the perceptual experience in words). The bulk of Gilson's book is designed to illustrate the philosophical experience by tracing the fate of certain philosophical ideas through history. He argues that the three greatest metaphysicians--Plato, Aristotle, and St. Thomas--came closest to expressing a pure philosophical experience in their philosophy because they understood that philosophy must be done philosophically. That might sound like a truism, but Gilson's history illustrates how easy it is to miss that truth. Descartes, for example, missed it when he attempted to solve philosophical problems by mathematical method. As soon as Descartes tried to substitute mathematics for philosophy, his failure was certain. The same was true for Ockham's use of logic, Kant's use of physics, and Comte's use of sociology. Each of them tempered the philosophical experience with some other kind of experience--the mathematical, logical, etc. The result of this tempering led Descartes, Ockham, et al. to neglect Being, to the detriment of their philosophy. This is not to say that Descartes's philosophy is not philosophy at all, but that his philosophy is flawed because it neglects the unifying principle of philosophy, namely, Being.
I think, when supplemented with some primary texts in philosophy, this would make an excellent book for an introduction to philosophy class. It is not a comprehensive history, but I don't think a comprehensive work would necessarily be the best work for such a class. In fact, such a work might even neglect Gilson's lesson.