In 1848, Laurens P. Hickok, then a Professor in Auburn Theological Seminary, published a work entitled "Rational Psychology," in which he professed to establish, by _a priori_ processes, positions which, if true, afford a ground for the answer, at once and forever, of all the difficulties raised by Sir William Hamilton and his school. Being comparatively a new writer, his work attracted only a moiety of the attention it should have done. It was too much like Analytical Geometry and Calculus for the popular mind, or even for any but a few patient thinkers. For them it was marrow and fatness. Since the followers of Sir William Hamilton, whom we will hereafter term Limitists, have neglected to take the great truths enunciated by the American metaphysician, and apply them to their own system, and so be convinced by their own study of the worthlessness of that system, it becomes their opponents, in the interest of truth, to perform this work in their stead; viz., upon the basis of immutable truth, to unravel each of their well-knit sophistries, to show to the world that it may "_know the truth_;" and thus to destroy a system which, if allowed undisputed sway, would sap the very foundations of Christian faith. The philosophical system of the Limitists is built upon a single fundamental proposition, which carries all their deductions with it. He who would strike these effectually, must aim his blow, and give it with all his might, straight at that one object; sure that if he destroys that, the destruction of the whole fabric is involved therein. But, as the Limitists are determined not to confess the dissolution of their scheme, by the simple establishment of principles, which they cannot prove false, and which, if true, involve the absurdity of their own tenets, it is further necessary to go through their writings, and examine them passage by passage, and show the fallacy of each. In the former direction we can but re-utter some of the principles of the great American teacher. In the latter there is room for new effort; and this shall be our especial province.