If and when the scientist who observes phenomena and tabulates facts tries to sink a shaft deep down through them, he will strike the stratum of metaphysics. He may despise it, he may withdraw in disgust, but if he continues to push his shaft he will not be able to escape having to investigate his phenomena and facts in the way that the metaphysician investigates them. Nor will he be able to stop even there. If first thought makes a common man into a scientist, and second thought into a metaphysician, third thought will make him into a philosopher.
-- Notebooks Category 7: The Intellect > Chapter 6: Science > # 101