On the first page of Karl Ameriks book, Kant and the Fate of Autonomy, he cite Rottgers:
How it could happen that a whole epoch of philosophers, from Reinhold to Hegel, was of the opinion that philosophy must be deduced from a single proposition—this has remained unclear to me, and I have as yet found no answer for it in the literature.
An interesting question, but this post is not about Ameriks observation. It’s nearing the end of the semester and it’s about that time in which I’ll pose a series of annoying questions to my students: What is philosophy? What should philosophy concern itself with? How should one philosophize? etc. to tie up the course. Since I’m teaching the first of the three essays in Nietzsche’s Genealogy of Morals, I was thinking this morning about his insistence that the good–in the good/evil binary–can only emerge at the expense (or exclusion) of its opposite, whose quality is conceptually prior to, and wholly independent of the “good.” From the get go, hasn’t philosophy been defined by that which it excludes? In Nietzsche’s sense above, philosophy only arrives at its definition through the refusal of its opposite, but moreover, it ends up giving priority to that which it refuses. In this sense, philosophy is essentially an afterthought. Along the lines of Nietzsche’s analysis of morality, the “business” and the origins of philosophy, I was reminded of the opening lines of Franz Rosenzweig’s Star of Redemption:
From death, it is from the fear of death that all cognition of the All begins. Philosophy has the audacity to cast off the fear of the earthly, to remove from death its poisonous sting, from Hades his pestilential breath.
I’m not going to rehash the whole of Rosenzweig’s introduction to the Star, but he reads the history of philosophy, from Socrates to Nietzsche (though Nietzsche is able to take a step in the right direction), as a type of suicide. As Rosenzweig sees it, Plato chose to avoid facing fear of death by refusing the materiality of life by positing an Ideal reality. Such other-worldliness –suggests Rosenzweig–permeates the whole of philosophy. Philosophy seems to always be in some sort of “crisis” or is always seeking to (re)define itself (I can’t help but think of Mikhail’s assessment of the history of philosophy morphing into the history of enemies here). This makes perfect sense given the above. However, until it stops defining itself through what it refuses, we’ll never have arrived at a satisfactory definition of philosophy, how to philosophize and what philosophy should concern itself with. It’s like the snake that eats itself. Or maybe I’m just being cranky.
Perverse Egalitarianism 
Interesting ideas. I only want to comment on the first and the last. Fred Beiser’s German Idealism: The Stuggle Against Subjectivism is good on this search for a single principle, though he reads the early post-Kantians differently from what seems to be suggested above (I need to look at Ameriks again to be sure), saying that the preoccupation with a single principle was less widespread than some scholars think. Yes, it’s in Reinhold (for a period, Reinhold seems to have changed his philosophy more often than his socks) and in Fichte and even briefly in Schelling, but that’s about it. The Grundsatzkritik put paid to the plausibility of it, and the Absolute (the only principle to survive this debate, because it is in a sense not a principle) was shifted from being first to being last, a possibility.
On the closing idea, yes, I’ve been thinking of this too, though in a different sense. When the idea of the history of philosophy changes from being a history of partially correct attempts (Hegel) to being the history of a pernicious or lamentable error (Nietzsche, Heidegger, much 20thC philosophy) then ‘enemies’ will start to appear everywhere, and whole epochs and movements can be passed over as vast mistakes. Which would itself be a mistake. The academy, not immune to such views of the history of philosophy (which are also views of philosophy per se), assimilates them into the curriculum such that we get whole generations who, following Heidegger for example (because they have been taught Heidegger), have learned little about, say, German Idealism, and have to work to catch up.
I’m pretty sure Nietzsche wanted to evoke the fearless warrior he never was and cultivate strange attitudes in a universe that was thought to be a big mechanism. Dostojevsky depicted some characters who proofed their independence from material conditions and a rationally determined world by committing crimes and becoming weird.
At any time there is a Zeitgeist substrate which remains in the background of a thinkers work. Who is really concerned today about Laplacian determinism and the metaphor of a ( dead ) world as a clock which is the ultimate horror and has to be avoided at all costs by the invention of a fancy, crazy, self-determined, vital, contingent subject? Maybe objectologists who converted this quibbling subject into objects in order to save the objects soul ( or reality ) from the perils of science.
At the same time the masochist attempt to copy the Euclidean style of derivation of anything from fist premises. After the work of Bolyai and Lobatschewski which busted this paradigm it only haunted mathematics for another century until it got finally killed by Kurt Gödel. Today it is only a working economy of interest, thought and description, nothing metaphysically deep.
If there was a merit in postmodernism than it is the eager attempt to define the Zeitgeist, an intellectual subconscious, a distributed esprit, a field of signification as Foucault attendees would likely put it. Neither the work of an individual nor that of a distinguishable collective. Nietzsche was one of the pioneers as an “Unzeitgemäßer” – of course, in retrospective he was a very timely non-conformist.
BTW if the “fear of death” was ever so strong why was the invention of the hell necessary? Seems like the fear of a horrible life in pain is bigger than that of a quiet non-existence.