Philosophy is unlike any other subject. It studies the core of human understanding (philosophy of psychology) and knowledge (epistemology), but also how we reason that knowledge (philosophy of logic), and record and communicate it (philosophy of language). It explores our social fabric (social and political philosophy), but also the fabrics of the theoretical: space and time beyond what we see (philosophy of metaphysics); and then some.
I have some fond stories of my 'bible'. Once — late last year — I was quite sick, unable to read anything. Naturally I was bored out of my mind. I eventually picked up my Oxford Companion to Philosophy and began reading. Lo and behold I read for nearly two hours and only stopped once I realized I'd been reading in an awkward position with my neck arched downward. I get lost in this tome of thought all the time. Anyways, the Oxford Companion to Philosophy is full of thought-worthy, provocative, informative, and all around interesting entries ranging from the big names to the small, the widely-known ideas to the lesser-known, and so on.
The Companion features over 2,200 entries, including some 300 new to this 2005 edition (the first edition was issued a decade earlier), 291 contributors, and covers everything and everyone from "animal consciousness" to "David Hume" to "God, arguments for the existence of" (and an entry of "arguments against the existence of") to "zombies". There are some illustrations, and articles can be a small paragraph or several pages. There are also references and books to see for more information listed at the end of virtually every entry. Plus, diagrams chart out the various main branches of philosophy in the back of the book, followed by a complete cross-index, all being preceded by a nice chronology of philosophy.
However not everything can fit in what is seen as the definitive one-volume philosophy reference book. I have compiled a list of entries my bible is lacking — including "negative utopia", "George Orwell", "Big Brother" (yes I like George Orwell, a lot), "A.C. Grayling", "Eric Hoffer" and more — and will email the editor and publisher once I'm sure I have thought of everything.
The website of Oxford University Press (OUP), the book's publisher, states that the book's readership is targeted at:
General readers interested in abstract thought, the eternal questions, and the foundations of human understanding; students and professionals in philosophy and related fields (physical, human, and social sciences, the arts and humanities).
The book runs about US$60, but you can easily find it for cheaper (see Amazon). I keep my bible handy at all times; I take on vacation (when I can). It's a great book; anyone interested in more advanced thought than portrayed by tabloids and celebrity rags, not to mention the often shallow politics of the day, should check it out. It's one of those books that you keep for a lifetime.