"Here then is the only expedient, from which we can hope for success in our philosophical researches, to leave the tedious lingering method, which we have hitherto followed, and instead of taking now and then a castle or village on the frontier, to march up directly to the capital or centre of these sciences, to human nature itself; which being once masters of, we may everywhere else hope for an easy victory. From this station we may extend our conquests over all those sciences which more intimately concern human life, and may afterwards proceed at leisure to discover more fully those which are the objects of pure curiosity. There is no question of importance, whose decision is not comprised in the science of man; and there is none, which can be decided with any certainty, before we become acquainted with that science. In pretending, therefore, to explain the principles of human nature, we in effect propose a complete system of the sciences, built on a foundation almost entirely new, and the only one upon which they can stand with any security."[49] Ibid. pp. 13-14. The present writer has a special interest in citing these passages, because they do in fact defend as well as describe the procedure of his very next chapter. Such then at an early age was Hume's keen-edged critical appreciation of those intellectual conditions required for a Philosophy of the Sciences, or as he calls it, the "true Metaphysics." In order to supplement his clever and clear idea by a very practical delineation of the metaphysical territory, we turn to another great thinker, the founder of our modern natural science, the great Lord Verulam.[50] Bacon divides Philosophy according to its objects, which are three,--God, Nature, Man. Take, then, Natural Philosophy; it is well said that the truth of nature lies deeply hidden, and it is also well said that the Producer imitates Nature. Natural Philosophy divides itself accordingly into the inquisition of causes and the production of effects; it is both speculative and operative. There is indeed an intercourse between causes and effects, and both these kinds of knowledge. All true and fruitful Natural Philosophy has a double scale or ladder,--ascendent and descendent; ascending from experiment to first causes; descending thence to fresh experiment and always fresh productiveness.[51]