QUOTE : The three greatest metaphysicians who ever existed - Plato, Aristotle and St.Thomas Aquinas - had no system in the idealistic sense of the word. Their ambition was not to achieve philosophy once and for all, but to maintain it and to serve it in their own times, as we have to maintain it and to serve it in ours. For us, as for them, the great thing is not to achieve a system of the world as if being could be deduced from thought, but to relate reality, as we know it, to the permanent principles in whose light all the changing problems of science, of ethics and of art have to be solved. A metaphysics of existence cannot be a system wherewith to get rid of philosophy, it is an always open inquiry, whose conclusions are both always the same and always new, because it is conducted under the guidance of immutable principles, which will never exhaust experience, or be themselves exhausted by it. For even though, as is impossible, all that which exists were known to us, existence itself would still remain a mystery. Why, asked Leibniz, is there something rather than nothing ?