And this is the distinctive problem of rational theology. Philosophy and science both lead up to theology as the apex of human knowledge. The latter may be fitly called the _scientia scientiarum_. Questions as to the nature and origin of Life upon our planet, the nature of Force or energy, the problems of Substance and of Cause, the questions of the Absolute and Infinite, all centre in this, are all the several ways of expressing it from the point of view which the questioner occupies, 'What is the ultimate principle of the universe, the ἀρχὴ of all existence?' Speculative philosophy and science deal proximately, it is true, with the problems of finite existence, existence as presented to us in the surrounding universe, and the laws which regulate it; but they covertly imply and remotely lead up to the question we have stated. They are the several approaches to that science which sits enthroned on the very summit of human knowledge. Nevertheless, the science of speculative theology is as yet lamentably incomplete. We have scores of treatises devoted to the subject, and numerous professed solutions of the problem. But we have not, in the English language, a single treatise which even contemplates a philosophical arrangement and classification of the various theories, actual and possible, upon the subject. It is otherwise with the great questions of intellectual and ethical philosophy. We have elaborate and almost exhaustive schemes of theories on the nature of perception, or our knowledge of the external world, the laws of association, the problem of causality, and the nature of conscience. But we look in vain for any similar attempt to classify the several lines of argument, or possible modes of theistic proof, so as to present a tabular view of the various doctrines on this subject. We are limited to the well-known but precarious scheme of proofs _à priori_ and _à posteriori_,[11] and to the more accurate classification of Kant, the ontological, the cosmological, and the physico-theological proofs, with his own argument from the moral faculty or practical reason. In addition, we are not aware of any English treatise specially devoted to the history of this branch of philosophical literature, with the exception of a brief essay by Dr. Waterland, in which he traverses a small section of the whole area; and that not as the historian of philosophical opinion, but in the interest of a special theory.[12]