A final difficulty against philosophical research is suggested by the thought that if the philosopher has to take cognizance of all the conclusions of all the special sciences his task is an impossible one, inasmuch as nowadays at all events it would take a lifetime to become proficient in a few of these sciences not to speak of all of them. There is no question, however, of becoming proficient in them; the philosopher need not be a specialist in any positive science; his acquaintance with the contents of these sciences need extend no farther than such established conclusions and such current though unverified hypotheses as have an immediate bearing on ultimate or philosophical problems. Moreover, while it would be injurious both to philosophy and to science, as is proved by the history of both alike, to separate synthetic from analytic speculation by a divorce between philosophy and science; while it would be unwise to ignore the conclusions of the special sciences and to base philosophical research _exclusively_ on the data of the plain man’s common and unanalysed experience, it must be remembered on the other hand that the most fundamental truths of speculative and practical philosophy, the truths that are most important for the right and proper orientation of human life, can be established and defended independently of the special researches of the positive sciences. The human mind had not to await the discovery of radium in order to prove the existence of God. Such supreme truths as the existence of God, the immortality of the human soul, the freedom of the human will, the existence of a moral law, the distinction between right and wrong, etc., have been _always_ in possession of the human race. It has been, moreover, confirmed in its possession of them by Divine Revelation. And it has not needed either the rise or the progress of modern science to defend them. These fundamental rational truths constitute a _philosophia perennis_: a fund of truth which is, like all truth, _immutable_, though our human insight into it may develop in depth and clearness. But while this is so it is none the less true that philosophy, to be progressive in its own order, must take account of every new fact and conclusion brought to light in every department of scientific—and historical, and artistic, and literary, and every other sort of—research. And this for the simple reason that every such accession, whether of fact or of theory, is an enlargement of human experience; as such it clamours on the one hand for philosophical interpretation, for explanation in the light of what we know already about the ultimate grounds and causes of things, for admission into our world-outlook, for adjustment and co-ordination with the previous contents of the latter; while, on the other hand, by its very appearance on the horizon of human experience it may enrich or illumine, rectify or otherwise influence, this outlook or some aspect of it.(42)