How original can a philosopher's philosophy be? If it were utterly original (i.e., if it had no links to any previous philosophy), then perhaps it wouldn't be philosophy at all.
Take the “radicals” in the tradition of analytic philosophy.
Eliminative materialists and “anti-realists”, for example, needed to share some kind of a philosophical language with their contemporaries (as well as with the tradition), otherwise their chosen language and positions would have been inscrutable.
Perhaps at another possible world there are other philosophies which are completely alien to our own. We can now ask:
Why are “alien philosophies” philosophies at all if they share nothing with our own philosophies – i.e., if they're truly alien?
Schopenhauer once asked the following question (to paraphrase):
Why do philosophers never step outside books [or “texts”]?
Schopenhauer was very critical of the parasitical nature (as he saw it) of much philosophy. That is, he was critical of philosophers' reliance on other philosophers' texts. This was a philosophical point about what some Continental philosophers have called “intertextuality”. This term itself was coined by Julia Kristeva. However, let the semiotician Roland Barthes explain it:
“Any text is a new tissue of past citations. Bits of code, formulae, rhythmic models, fragments of social languages, etc. pass into the text and are redistributed within it, for there is always language before and around the text. Intertextuality, the condition of any text whatsoever, cannot, of course, be reduced to a problem of sources or influences; the intertext is a general field of anonymous formulae whose origin can scarcely ever be located; of unconscious or automatic quotations, given without quotation marks.”
Thus if Schopenhauer had spoken in contemporary terms, he might have said that (philosophically speaking) intertextual webs trap philosophers within them .
In response, the post-structuralist/deconstructor Jacques Derrida might have said that Schopenhauer was fooling himself if he really believed that he could escape from all the webs - or snares - of intertextuality. Derrida believed that we're all trapped within them (at least all Westerners are). And, as the fictional deconstructing car mechanic said to the analytic philosopher John Searle: "There is nothing outside the text.” (Il n'y a pas de hors-texte. - The apparently “correct” translation of Derrida's French doesn't help either.)
Philosophy Ex Nihilo
What would a philosophical a priori (as it were) be like? A philosophy untouched by other philosophies - untouched by other philosophical texts? Take the British broadcaster, politician and populariser of philosophy, Bryan Magee, and his account of his own ex nihilo philosophising:
“Until I went to university it never entered my head to associate any of these [philosophical] questions with the word 'philosophy'…I discovered that this is what they were…I had grown up a natural Kantian… I discovered…that I had been immersed in philosophical problems all my life.” [From Magee's Confessions of a Philosopher: A Journey Through Western Philosophy.]
What a strange passage that is. Magee wasn't claiming to be "outside language"; though he was claiming to have been outside philosophy. He was claiming that all of us are born with a kind of quasi-Chomskian Philosophy Faculty. However, if he wasn't claiming something about a universal philosophy faculty, then Magee must have been making a claim about himself - and himself alone. That claim must therefore be that Magee was somehow genetically programmed to philosophise in the particular manner in which he did in fact philosophise.
If the first option is taken (i.e., the quasi-Chomskian philosophising faculty), then many - if not all - young children (throughout the world) would be asking the same questions which Magee asked himself when he was a young child. It's of course true that many children do indeed ask philosophical questions. So which questions and problems was Magee talking about?
As Magee put it, he asked himself questions which he later realised were Kantian, Schopenhauerian, Leibnizian and Wittgensteinian in nature. If that's the case, then why weren't Kantian and Leibnizian - never mind Wittgensteinian - problems raised years before the birth of these particular philosophers? If these questions and problems are so natural (Magee claimed to be a "natural Kantian"), then why are they certainly not asked in other cultures in our own time (that's unless they come into contact with Western philosophy)? There may indeed be certain philosophical givens. (The American philosopher Thomas Nagel - in his book The Last Word - believes this to be the case.) Nonetheless, they certainly aren't, say, Kantian or Wittgensteinian givens. And any any givens (uncovered by empirical research) tend to be more theological, mystical or spiritual in nature; rather than (strictly speaking) philosophical.
It's of course possible that Magee was an incredible genius who not only came to Kantian questions and problems without the help of Kant; but to Leibnizian and Wittgensteinian problems and questions without their help too! (Rather modestly, Magee did claim that he didn't find "solutions for them".)
In the end it will be empirical research which will determine whether or not Kantian, Leibnizian, etc. problems and questions are really part of the philosophical a priori. From my own knowledge and reflections, I suspect that they aren't. Despite saying that, this doesn't devalue such philosophy in any way.
So where did Kant's Kantian problems and questions come from?They largely came from other philosophers. And where did Leibniz’s Leibnizian problems come from? Ditto.
More clearly, Kant wouldn't have been a Kantian (ostensibly unlike Magee) without the problem of the impasse between Rationalism and Empiricism; as well as the scepticism of Hume. Schopenhauer wouldn't have been a Schopenhauerian (again, unlike Magee) without Kant and the work of the German Idealists who came before him (among other things).
Thus perhaps Magee simply felt inclined to squeeze his own childhood questions and problems into a Kantian hole.
Schopenhauer also saw himself in the way in which Magee saw himself. In other words, he saw himself as a kind of aprioristic philosopher. So Schopenhauer didn't only take a position on the a priori within philosophy; but also an a priori position towards philosophy itself. He thought that the best way to do philosophy isn't to read philosophical texts. Instead, it's simply to think and reason independently. (Wittgenstein also claimed this!)
Yet in his early life Schopenhauer confessed to being more or less obsessed with Kant. This must surely mean that Schopenhauer simply took an independent position on philosophy after the fact. He was like a car driver in a long car race who drives a car with an extra large petrol tank filled up to the brim. A driver who then claims to his fellow competitors that his car doesn't need any extra petrol. Yet, of course Schopenhauer partly - or even largely - lived off his memories of other philosophers' texts.
As for intertextuality as it applies to other philosophers.
Take William G. Lycan’s medium-length paper ‘The Continuity of Levels of Nature’: it includes fifty-two references to other philosophers’ texts. And, in addition, Jaegwon Kim’s ‘Supervenience as a Philosophical Concept’ has fifty-one such references.
And since two analytic philosophers have just been mentioned, it can be said that when a student of analytic philosopher thinks about the nature of the mind, all he primarily does is read and think about what, for example, Jerry Fodor and Daniel Dennett have said about the nature of mind. This must mean that he too may well be caught in his own intertextual trap. (Though, of course, it’s unlikely that any philosopher of mind would rely on just two philosophers of mind.) Indeed all his responses, reactions and commentaries on the nature of mind may also be largely intertextual in nature.
Thus when students study philosophy at university, it seems that reading texts often seems far more important than independent thinking and reasoning. Isn't this called “research”?
On the other hand, many philosophers (or wannabe philosophers) would like to flatter themselves with the view that their own philosophical views have occurred ex nihilo. However, genuine ex nihilo philosophical thought may be as unlikely as ex nihilo mental volition or action (what philosophers call “origination”). As I said, there may be some cognitive givens; though whether or not they're truly philosophical is open to debate. They certainly aren't Kantian or Wittgensteinian givens.
It can be asked where would the novice aprioristic philosopher get his concepts and tools from? Isn't it the case that he wouldn’t have the vocabulary to philosophise in the first place? Isn't it also the case that he wouldn’t even feel the need to ask philosophical questions without the spur of preceding philosophy?
As Derrida put it (in his 'Violence and Metaphysics' ) in a slightly different context (as well as to paraphrase):
The apriorist philosopher would still think or speak Greek.
Derrida himself - despite his deconstructions! - admitted to being a “Jew-Greek”. He said that he lived in a “house” which had been built for him by (religious) Jews and Christians; as well as by philosophical Greeks.