"... For this feeling of wonder shows that you are a philosopher, since wonder is the only beginning of philosophy" (Plato, Theaetetus 155d)
"... It is through wonder that men now begin and originally began to philosophize" (Aristotle, Metaphysics 1, 3, 2).
The meaning of the word philosophy is 'systematic or methodical research, research into truth and the nature of things'. The Greeks began very early to wonder about the world round them, and to try and explain how it started. The first to try were the natural philosophers from Ionia. Later on, as laws and (in particular) law courts became normal, it was necessary to arrive at a definition of what was good (or evil), of responsability for one's actions, and so on. This gave rise to the so-called 'practical philosophers', the Sophists, who interpreted on the principle that "circumstances alter cases". It was not until the very end of the 5th century B.C. that the time was ripe for a metaphysical interpretation of life's basic concepts. The leaders here were Plato and, in Plato's wake, Aristotle. This was when philosophy acquired the meaning it still has today.