In the eighteenth century there were elaborated a great many proofs which claimed to be _a priori_ theistic demonstrations based on the notions of existence and causality. Assuming that something is, and that nothing cannot be the cause of something, these arguments attempted to establish that there must be an unoriginated Being of infinite perfection, and possessed of the attributes which we ascribe to God. The most famous of them was, perhaps, that of Dr Samuel Clarke, contained in the Boyle Lecture of 1704. But Dr Richard Fiddes, the Rev. Colin Campbell, Mr Wollaston, Moses Lowman, the Chevalier Ramsay, Dean Hamilton, and many others, devised ingenious demonstrations of a similar nature. It is impossible for me to discuss here their merits and demerits. Probably not one of them has completely satisfied more than a few speculative minds. They are certainly not fitted to carry conviction to the ordinary practical understanding. Yet it is not easy to detect flaws in some of them; and the more carefully they are studied, the more, I am inclined to think, will it be recognised that they are pervaded by a substantial vein of truth. They attempted logically to evolve what was implied in certain primary intuitions or fundamental conditions of the mind, and although they may not have accomplished all that they aimed at, they have at least succeeded in showing that unless there exists an eternal, infinite, and unconditioned Being, the human mind is, in its ultimate principles, self-contradictory and delusive.[49] [49] See Appendix XXXVIII.