[for a brief explanation of this ongoing series, as well as a full table of contents, go here]
“Wonder is the feeling of the philosopher, and philosophy begins in wonder.” (Plato)
The central thesis of this book is that philosophy, in a non-trivial sense, makes progress, although that sense is significantly different from that of scientific progress and — I will argue — somewhere closer to progress in mathematics and logic. 
My interest in this question arises from a somewhat unusual academic path. I began my career as an evolutionary biologist, with an interest in gene-environment interactions (what philosophers typically refer to as nature-nurture questions). I pursued both empirical and theoretical research in that field for about a quarter of a century, and then decided that I needed to do something different. Armed with a freshly acquired degree in philosophy and a published thesis in philosophy of science (Pigliucci and Kaplan 2006) I eventually landed a job as a full time philosopher. And then the trouble began.
I quickly learned — though it should have come as no surprise, really — that philosophers are an unusual bunch of academics, at least compared to scientists. Philosophers are overly prone to question the very foundations and utility of their own discipline, in some cases (as we shall see) even going as far as agreeing with some scientists who have a bit too hastily declared philosophy dead or useless (often, precisely on the alleged ground that it doesn’t make progress, or at least not the sort of progress a scientist expects). Add to this that philosophy has of late developed a significant PR problem, as we have just seen, both with the public at large and with other academics (again, particularly scientists), and we have the recipe for a generalized crisis within one of the oldest fields of inquiry that has ever occupied human minds.
I think much of this trouble is based on common misunderstandings about what philosophy is and how it works, and that it can (and ought) to be corrected, particularly, of course, by its own practitioners. Before getting any further, however, we need to address the question that we postponed from the previous chapter: what is philosophy? Again, this is the sort of thing that only philosophers indulge in asking, while practitioners of other disciplines are more than happy to go about their business without too much self-referential pondering (they would probably say without “wasting too much time”). Indeed, the whole field of metaphilosophy is dedicated to how philosophy itself works and, by implication at least, to what philosophical investigations consist of.
It is not easy to catch philosophers on record — especially in peer reviewed publications — freely musing about how to best characterize their field. But we live in a world in which even philosophers are getting used to social media, podcasts and blogs, and it turns out that such outlets are friendlier to our quest. So for instance, Popova (2012) collected a variety of responses to the question “What is Philosophy?” from a number of prominent contemporary practitioners, and some of the answers are illuminating.
For Marilyn Adams, for instance, the point is “trying to bring analytic clarity both to the questions and the answers,” while for Peter Adamson “Philosophy is the study of the costs and benefits that accrue when you take up a certain position.” Richard Bradley says that it is “about critical reflection on anything you care to be interested in,” whereas Allen Buchanan claims that it “generally involves being critical and reflective about things that most people take for granted.” Don Cupitt simply says that philosophy is concerned with critical thinking (an unfortunately much abused term, of late); for Clare Carlisle it is “about making sense of all of this [the world and our place in it]”; and Barry Smith agrees, saying that philosophizing is “thinking fundamentally clearly and well about the nature of reality and our place in it.” For Simon Blackburn philosophy is “a process of reflection on the deepest concepts,” something that Tony Coady describes as “a science of presuppositions.” For Donna Dickenson it is about “refusing to accept any platitudes or accepted wisdom without examining it”; Luciano Floridi talks about conceptual engineering, and Anthony Kenny refers to “thinking as clearly as possible about the most fundamental concepts that reach through all the disciplines.” For Brian Leiter — arguably the most influential (and controversial) professional philosopher who blogs — a philosopher is someone who “creates new ways of evaluating things — what’s important, what’s worthwhile,” and Alexander Nehemas candidly tells us that he became a philosopher “because I wanted to be able to talk about many, many things, ideally with knowledge, but sometimes not quite the amount of knowledge that I would need if I were to be a specialist in them.” For my CUNY colleague David Papineau philosophy “requires an untangling of presuppositions: figuring out that our thinking is being driven by ideas we didn’t even realize that we had,” while Janet Radcliffe Richards regards “philosophy as a mode of enquiry rather than a particular set of subjects … involving the kind of questions where you are not trying to find … whether your ideas are true or not, in the way that science is doing, but more about how your ideas hang together.” Michael Sandel, a veritable star of public philosophy, opines that philosophizing means “reflecting critically on the way things are. That includes reflecting critically on social and political and economic arrangements. It always intimates the possibility that things could be other than they are.” Finally, Jonathan Wolff identifies philosophical problems as those that “arise … where two common-sense notions push in different directions, and then philosophy gets started.” (The survey also reported somewhat uninformative or purely poetic concepts of philosophy, such as “Philosophy is the successful love of thinking,” or “When nobody asks me about it, I know. But whenever somebody asks me about what the concept of time is, I realize I don’t know,” for which — I have to admit — I have little patience.)
Obviously, the above survey is entirely informal and biased in a number of ways (particularly toward Western philosophers, many close to the so-called analytic tradition — more on this below), but then again, there does not seem to be much call for social science inquiries into the thought patterns of philosophers (with the exception of some “experimental philosophy,” to which we’ll get in due time). Still, when I read the above and other definitions included in Popova’s informal survey I actually felt encouraged. Despite the tendency to exaggerate differences, there are obvious threads emerging from the opinions of the various philosophers interviewed.
Indeed, the above is essentially a summary of what I — naively — thought of philosophy before approaching the field professionally: it is about reason, logic, arguments and analysis, not empirical evidence per se, though of course it better be informed by the best of what we know of how the world works, particularly from science; it is about examining common notions and discovering that they are more complex than often thought, or perhaps even arriving at the conclusion that they are incoherent; it is about the kind of broad thinking that helps us understand our reality as human beings in the vast universe described by science; and it has practical consequences for how we conduct our lives and structure our societies. In a sense, then, philosophy is a family resemblance, or cluster, concept, in the way Wittgenstein (1953, #65-69) thought many interesting human concepts are (including, as we have seen in the Introduction, the concept of progress!).
But, the properly skeptical philosopher may argue, there is a lot more to philosophy, and many more ways of philosophizing, than the little summary above hints at. In fact, even the inherent flexibility of a Wittgensteinian cluster concept may seem inadequate once we consider the differences between, say, analytic and continental philosophy, the two major “modes” in which the profession has split itself throughout the 20th century. This split, incidentally, has been questioned and downplayed of late, and it has always been far less sharp than often assumed. Nonetheless, there are important differences of style and subject matter between philosophers who express themselves within those two modes of inquiry, so I retain and discuss that distinction below. And then there is, of course, the difference between Western style, Greek-descended, philosophy and Eastern philosophies, which are in themselves incredibly diverse, with Indian, Chinese, Japanese and other traditions branching off each other, and yet overlapping among themselves and with the traditions of the West. Not to mention Islamic philosophy, African philosophy, etc. The list goes on.
This objection is to some extent appropriate, and the rest of this chapter is my way of dealing with it. I will argue in the following that my project needs to be limited to Western philosophy as classically understood, as well as to any tradition — be it internal to the West but of a “continental” flavor, or be it external, Eastern, Islamic or African — that sufficiently resembles it. This is not a value judgment, but a simple recognition of the fact that some of the activities that go under the broader aegis of “philosophy” are intellectual enterprises of a different enough nature that they need to be considered in their own right, and possibly be attributed a different name (being that the term φιλοσοφία originally used by the Greeks is already taken).
Before considering the differences between analytic and continental philosophy, as well as between the Western and Eastern traditions, however, let us entertain a novel and likely unfamiliar to philosophers, approach to the question. In what follows I enlisted the help of Simon Raper, a contributor to “Drunks&Lampposts.” Simon was as curious as I to figure out whether there is quantitative evidence of the much-talked about differences and relationships among various schools of (largely Western, in this case) philosophy. So he enlisted two 21st century resources in a particularly ingenious fashion. First, he downloaded a file containing all the “influenced by” links for every philosopher listed on Wikipedia.  He then used a program called Gephi, an open software graphing platform, to visualize the influences among philosophers in the form of a network with the size of individual entries (say, for Aristotle) proportional to how many connections to other philosophers they have. Finally, Simon was able to provisionally identify different “schools” of thought by asking the program to depict in different colors groups of people whose within-cluster connections were significantly stronger than the connections to other groups. (If this sounds a lot like the Digital Humanities, it’s because it is. But let’s wait until later in the book to debate the pros and cons of the particular approach.)
The results are visually stunning and they actually confirm what most professional philosophers might have told you beforehand. (Although this may be somewhat disappointing, I choose to interpret the outcome as confirming that the opinions of historians of philosophy are actually well grounded quantitatively. There goes the scientist in me.) For instance, Figure 1 shows the broadest possible picture, were therefore few of the details are visible. But one can immediately discern classical philosophers (Aristotle, Plato, all the way to Descartes), continental and proto-continental ones (Hegel, Nietzsche, Heidegger, Sartre), analytical and proto-analytical fellows (Hume, Mill, Russell), as well as crucial transitional figures (chiefly Kant and Wittgenstein). 
Figure 2 is a close up of the continental tradition, where Hegel and Nietzsche loom largest, followed in importance (as measured, remember, by the number of connections to others — no intrinsic value judgment is implied here) by Kierkegaard, Husserl, Heidegger, Sartre, and Arendt and, to a lesser extent, by Foucault, Derrida and others.
Finally, Figure 3 shows the area of the connectogram occupied by British empiricism, American pragmatism, and the modern analytical tradition. Here we clearly see the towering influence of Hume and Wittgenstein mentioned above, followed by figures like Locke, Mill, Russell, James and, interestingly, Chomsky.
With this bird’s eye view in mind, let us now turn to a more traditional, peer-opinion based, discussion of the different ways of doing philosophy and how they may or may not constitute a coherent body (as I mentioned above, I do not think they do, which is why for the rest of the book I will limit myself to a subset of that larger set). It should go without saying it, but I hope the reader is not expecting an in-depth treatment of either the analytical-continental divide or, much less, of the differences between Western and Eastern philosophies (and I am not even touching the Islamic and African traditions, with which I am unfortunately much less familiar. I hope someone else will take up that task). Each one of those endeavors, to be conducted properly, would require a book-length treatment in its own right. In this chapter, and really throughout the book, I will instead trade in-depth analysis for a broad perspective, with all the advantages and pitfalls that such a strategic decision usually implies. End of the necessary apologia.
 Of course, it would be perfectly legitimate to claim logic as a branch of philosophy, show that the former makes progress and therefore claim that philosophy does too. But that would be too easy, and I prefer challenging propositions.
 I can see some of my esteemed colleagues rolling their eyes at the very mention of Wikipedia. Relax. First, the available empirical evidence is actually that — at least as far as science entries are concerned (and there is little reason to think that philosophical ones are different) — Wikipedia is about as accurate as the Encyclopedia Britannica (Giles 2005). Second, the data I am about to present is merely meant as illustrative of the possibilities, as such a study could be replicated using more scholarly sources, such as the Stanford Encyclopedia of Philosophy.
 I recognize that the terms “proto-continental” and “proto-analytical” are not part of the standard philosophical jargon. Consider them my modest contribution to the debate. I am confident that my fellow philosophers will recognize immediately why certain figures do indeed belong to those (albeit fuzzy) categories.
Giles, J. (2005) Internet encyclopaedias go head to head. Nature 438:900-901.
Pigliucci, M. and Kaplan, J. (2006) Making Sense of Evolution: The Conceptual Foundations of Evolutionary Biology. University of Chicago Press.
Popova, M. (2012) What is Philosophy? An Omnibus of Definitions from Prominent Philosophers (accessed on 26 June 2012).
Wittgenstein, L. (1953 / 2009) Philosophical Investigations. Wiley-Blackwell.