It would still remain a science of demonstration, with all its principles and rules of investigation unchanged. So with the doctrine of the Will. Whatever its bearings upon other sciences may be, it still remains no less exclusively a psychological science. It has its own principles and laws of investigation, principles and laws as independent of systems of theology, as the principles and laws of the science of optics are of those of Astronomy. In pursuing our investigations in all other departments of mental science, we, for the time being, cease to be theologians. We become mental philosophers. Why should the study of the Will be an exception? The question now returns--what should be the bearing of the fact, that our theory of the Will, whether right or wrong, will have an important influence in determining our system of theology? This surely should be its influence. It should induce in us great care and caution in our investigations in this department of mental science. We are laying the foundation of the most important edifice of which it ever entered into the heart of man to conceive--an edifice, all the parts, dimensions, and proportions of which, we are required most sedulously to conform to the "pattern shown us in the mount." Under such circumstances, who should not be admonished, that he should "dig deep, and lay his foundation upon a rock?" I will therefore, in view of what has been said above, earnestly bespeak four things of the reader of the following treatise. 1. That he read it as an honest, earnest inquirer after truth. 2. That he give that degree of attention to the work, that is requisite to an _understanding_ of it. 3. That when he dissents from any of its fundamental principles, he will distinctly state to his own mind the reason and ground of that dissent, and carefully investigate its validity. If these principles are wrong, such an investigation will render the truth more conspicuous to the mind, confirm the mind in the truth, and furnish it with means to overturn the opposite error.