To answer this, we must again refer to the fourth intuitive truth, viz., "the nature of a contrivance is proof of the intention or design of the author." This position is illustrated in many cases in common life. If we find a contrivance which moves the air toward a fire and thus increases the flame, we infer that the author intended to produce this result. If we find a contrivance to show the time of day, such as a sun-dial or clock, we can not help believing that the author intended to secure this end. Moreover, when we find a curious machine, where every part is arranged on a given design, we naturally inquire _how it must be worked_ to produce the intended result. It may have wheels that, if turned one way, produce the end designed, but, if turned another way, produce exactly the opposite effect. For example, if the wheels of a mill are arranged aright, or as the author designed, they will grind flour or weave cotton; but if arranged and worked contrary to the design of the author, they will break themselves to pieces and destroy all things around them. Two inquiries, then, are to be made in reference to the design of the Creator. The first is, What was the end or design for which he made all things? and the second is, What is the right and true method by which this design can be secured? We shall assume, and attempt to prove in what follows, that the design and ultimate end of the Creator in all his works is _to produce the greatest possible happiness with the least possible evil_. Afterward will be exhibited the _true and right method_ for securing this end, so far as we can learn it by reason and experience _without a revelation_. In pursuing this plan, the first step will be to exhibit the constitution and laws of mind, as the chief and most wonderful exhibition of the grand design of its Author. CHAPTER VII. DIVERSITIES IN SYSTEMS OF MENTAL PHILOSOPHY. We are now to commence an examination of the various powers and operations of the human mind, for the purpose of illustrating the grand aim of the Author in the creation of all things. In pursuing this course, it is needful, first, to refer to the apparent diversities in systems of mental philosophy, for the purpose of justifying the classification and the terms to be employed hereafter. There is nothing more hackneyed than the complaints against metaphysics as abstruse, difficult of comprehension, and unpractical, while the various writers on this science seem more or less divided into opposing schools. Notwithstanding this, there are reasons for maintaining a real agreement in all systems of mental philosophy, at least in essentials, and the following considerations lead to such a conclusion: