have ascertained the general characteristics of ultimate reality, and satisfied ourselves by careful analysis that reality, as conceived in our sciences, possesses those characteristics, that we have the right to pronounce our theory finally true. If Metaphysics should tum out in the end to present no fresh view as to the nature of the real, but only to confirm an old one, we should still, as metaphysicians, have the advantage of knowing where we were previously only entitled to conjecture. (3) The charge of unprogressiveness often brought against our science is easily disproved by careful study of the History of Philosophy. The problems of the metaphysician are no doubt, in a sense, always the same; but this is equally true of the problems of any other science. The methods by which the problems are attacked and the adequacy of the solutions they receive vary, from age to age, in close correspondence with the general development of science. Every great metaphysical conception has exercised its influence on the general history of science, and, in return, every important movement in science has affected the development of Metaphysics. Thus the revived interest in mechanical science, and the great progress made in that branch of knowledge which is so characteristic of the seventeenth century, more than anything else determined the philosophical method and results of Descartes; the Metaphysics of Leibnitz were profoundly affected by such scientific influences as the invention of the calculus, the recognition of the importance of _vis viva_ in dynamics, the contemporary discoveries of Leuwenhoeck in embryology; while, to come to our own time, the metaphysical speculation of the last half-century has constantly been revolving round the two great scientific ideas of the conservation of energy and the origin of species by gradual differentiation. The metaphysician could not if he would, and would not if he could, escape the duty of estimating the bearing of the great scientific theories of his time upon our ultimate conceptions of the nature of the world as a whole. Every fundamental advance in science thus calls for a restatement and reconsideration of the old metaphysical problems in the light of the new discovery.[8]