The work of the Philosophy of Nature and of Mind only begins where that of the experimental sciences leaves off. Its data are not particular facts, as directly amassed by experiment and observation, but the hypotheses used by experimental science for the co-ordination and description of those facts. And it examines these hypotheses, not with the object of modifying their structure so as to include new facts, or to include the old facts in a simpler form, but purely for the purpose of estimating their value as an account of ultimately real existence. Whether the hypotheses are adequate as implements for the calculation of natural processes is a question which Philosophy, when it understands its place, leaves entirely to the special sciences; whether they can claim to be more than useful formulæ for calculation, _i.e._ whether they give us knowledge of ultimate Reality, is a problem which can only be dealt with by the science which systematically analyses the meaning of reality, _i.e._ by Metaphysics. We may perhaps follow the usage of some recent writers in marking this difference of object by a difference in terminology, and say that the goal of experimental science is the Description of facts, the goal of Metaphysics their Interpretation. The difference of aim is, however, not ultimate. Description of facts, when once we cease to be content with such description as will subserve the purpose of calculation and call for description of the fact as it really is, of itself becomes metaphysical interpretation. The chief danger against which we must guard in this part of our metaphysical studies is that of expecting too much from our science. We could never, of course, hope for such a complete interpretation of facts as might be possible to omniscience. At most we can only expect to see in a general way how the physical and again how the psychical order must be thought of if our view as to the ultimate structure of Reality is sound. For an exact understanding of the way in which the details of physical and psychical existence are woven into the all-embracing pattern of the real, we must not look. And the value of even a general interpretation will of course depend largely upon our familiarity with the actual use the various sciences make of their hypotheses. With the best goodwill in the world we cannot hope to avoid all misapprehensions in dealing with the concepts of sciences with which we have no practical familiarity.