The doctrine of relativity derives its chief practical value from its connection with the next great doctrine of Hamilton's philosophy, the incognisability of the Absolute and the Infinite. For this doctrine brings Ontology into contact with Theology; and it is only in relation to theology that ontology acquires a practical importance. With respect to the other two "ideas of the pure reason," as Kant calls them, the human soul and the world, the question, whether we know them as realities or as phenomena, may assist us in dealing with certain metaphysical difficulties, but need not affect our practical conduct. For we have an immediate intuition of the attributes of mind and matter, at least as phenomenal objects, and by these intuitions may be tested the accuracy of the conceptions derived from them, sufficiently for all practical purposes. A man will equally avoid walking over a precipice, and is logically as consistent in avoiding it, whether he regard the precipice as a real thing, or as a mere phenomenon. But in the province of theology this is not the case. We have no immediate intuition of the Divine attributes, even as phenomena; we only infer their existence and nature from certain similar attributes of which we are immediately conscious in ourselves. And hence arises the question, How far does the similarity extend, and to what extent is the accuracy of our conceptions guaranteed by the intuition, not of the object to be conceived, but of something more or less nearly resembling it? But this is not all. Our knowledge of God, originally derived from personal consciousness, receives accession from two other sources--from the external world, as His work; and from revelation, as His word; and the conclusions derived from each have to be compared together. Should any discrepancy arise between them, are we at once warranted in rejecting one class of conclusions in favour of the other two, or two in favour of the third? or are we at liberty to say that our knowledge in respect of all alike is of such an imperfect and indirect character that we are warranted in believing that some reconciliation may exist, though our ignorance prevents us from discovering what it is? Here at least is a practical question of the very highest importance. In the early part of our previous remarks, we have endeavoured to show how this question has been answered by orthodox theologians of various ages, and how Sir W. Hamilton's philosophy supports that answer. We have now to consider Mr Mill's chapter of criticisms.