Question: How is – in our Western civilization which is dominated by the Greek tradition (Hellenism) and Christianity –, how is a non-Christian philosophy possible? This question is unanswerable; or rather, the answer must be: No, a non-Christian philosophy is not possible, there is none. 
– Josef Pieper, All philosophy is Christian
Philosophy is concerned with problems regarding existence, values, mind and language by a critical, systematic approach that relies on logical argument and reason. There are, of course, other approaches to thinking that rely more on persuasion, intuition, compromise, memorization, story-telling, religion, or mythology. There are even approaches to thinking that rely on logical argument and reason that are not considered philosophy, for example scientific thinking. Other approaches to thinking are less systematic and more spontaneous or creative, like poetry, music, and the fine arts. Learning is thinking, too. Learning is not philosophy. Some forms of thinking are systematic but do not require an argument, for example strategic thinking. Other forms of thinking are irrational or untruthful, yet they are just this: more thinking. Illogical or non-conclusive arguments are not considered philosophy, yet they are the products of thinking, too. And last, academic philosophy is distinguished from the activity philosophizing by a preset of technical terms and preexisting concepts, curriculum, and methodology that take years of study to internalize.
The following community text—in a ‘democracy,’ it is important what the masses know and told, is it not?—is a broad definition of what is considered ‘philosophy’ as far as Internet encyclopedianists are concerned:
Philosophy is distinguished from other ways of addressing fundamental questions (such as mysticism or mythology) or the arts by its critical, generally systematic approach and its reliance on reasoned argument.
There we encounter Ji Xianlin’s definition, again: That the philosophical approach to thinking ideally leads to system building. Just pondering over parts of another person’s philosophy does not constitute its own philosophy. Besides, only the creators of the most memorable philosophical systems –Plato, Immanuel Kant, David Hume, Georg W. F. Hegel, Karl Marx, for example– are venerated as great philosophers. Yet, no matter their initial novelty, to the best of our knowledge none of the great philosophers’ great philosophical systems – all purely intellectual inventions (we say: Vorstellungen or representations), no doubt – seemed to have passed the test of time.
In fact, bombastic philosophical systems –think Satre’s Existentialism, Freud’s Self, Levi-Strauss’s Structuralism, Meinong’s Ontology, Ayn Rand’s Objectivism, or Nietzsche’s Superhuman– come and go; and it is often the most easily impressionable students who take the rules in those systems as matter-of-fact, thus run into the dangers of growing up dogmatic and intolerant, the disciples and enablers of another person’s intellectual fantasy.
 Pieper, 2008: ‘Frage: Wie ist – in unserer westlichen Zivilisation, die vom Griechentum wie vom Christentum geprägt ist -, wie ist eine nicht-christliche Philosophie möglich? Diese Frage ist unbeantwortbar; oder vielmehr: die Antwort muß lauten: Nein, eine nicht-christliche Philosophie ist nicht möglich, es gibt keine.’
 Wikipedia, Philosophy, last access 02/2011
Pattberg, Thorsten (2011), Shengren – Above Philosophy and Beyond Religion, LoD Press, New York