It is indeed most extraordinary how long this distinction has held sway, or how it is the ablest men of all generations have quietly assumed that when once we know the natural causation of any phenomenon, we therefore know all about it--or, as it were, have removed it from the sphere of mystery altogether, when, in point of fact, we have only merged it in a much greater mystery than ever. But the answer to our astonishment how this distinction has managed to survive so long lies in the extraordinary effect of custom, which here seems to slay reason altogether; and the more a man busies himself with natural causes (e.g. in scientific research) the greater does this slavery to custom become, till at last he seems positively unable to perceive the real state of the case--regarding any rational thinking thereon as chimerical, so that the term 'meta-physical,' even in its etymological sense as super-sensuous or beyond physical causation, becomes a term of rational reproach. Obviously such a man has written himself down, if not an ass, at all events a creature wholly incapable of rationally treating any of the highest problems presented either by nature or by man. On any logical theory of Theism there can be no such distinction between 'natural' and 'supernatural' as is usually drawn, since on that theory all causation is but the action of the Divine Will. And if we draw any distinction between such action as 'immediate' or 'mediate,' we can only mean this as valid in relation to mankind--i.e. in relation to our experience. For, obviously, it would be wholly incompatible with pure agnosticism to suppose that we are capable of drawing any such distinction in relation to the Divine activity itself. Even apart from the theory of Theism, pure agnosticism must take it that the real distinction is not between natural and supernatural, but between the explicable and the inexplicable--meaning by those terms that which is and that which is not accountable by such causes as fall within the range of human observation. Or, in other words, the distinction is really between the observable and the unobservable causal processes of the universe. Although science is essentially engaged in explaining, her work is necessarily confined to the sphere of natural causation; beyond that sphere (i.e. the sensuous) she can explain nothing. In other words, even if she were able to explain the natural causation of everything, she would be unable to assign the ultimate _raison d'etre_ of anything. It is not my intention to write an essay on the nature of causality, or even to attempt a survey of the sundry theories which have been propounded on this subject by philosophers. Indeed, to attempt this would be little less than to write a history of philosophy itself. Nevertheless it is necessary for my purpose to make a few remarks touching the main branches of thought upon the matter[50].