_Connection of this Science with mental Discipline._--The importance of mental science may be further apparent in its effect on the culture and discipline of the mind. It is the peculiar effect of this science to sharpen and quicken the mental powers, to teach precision and exactness of thought and expression, to train the mind to habits of close attention and concentration of thought, to lead it to inquire into the causes and relations of things; in a word, to render it familiar with the great art of distinguishing things that differ. It would hardly be possible to name another branch of study that tends so directly to produce these results in the cultivation of the mind.
ANALYSIS AND CLASSIFICATION OF THE MENTAL POWERS.
_Importance of such a preliminary Investigation._--It is of the highest importance, as we approach a science like the one before us, to obtain, if possible, at the outset, a clear and comprehensive view of the field about to be explored. It is desirable that the traveller, before entering a new country, should learn something respecting its extent, its political and geographical divisions, its manners, its laws, its history. Even more necessary is it, in entering upon a new science, to know its boundaries and divisions, to obtain a clear idea, at the very commencement of our inquiries, of the number, nature, extent, and arrangement of the subject we are about to investigate. Otherwise we shall be liable to confusion and error, shall not know where, at any moment, in the wide field of investigation, we may chance to be, or what relation the topic of our immediate inquiry holds to the whole science before us; as a ship on the ocean, without observation and reckoning, loses her latitude and longitude. We shall be liable to confound those distinctions which are of less, with those which are of more importance, and to mistake the relation which the several topics of inquiry bear to each other. Especially is this previous survey and comprehension of the subject essential in a science like this, where so much depends on the clearness and accuracy with which we distinguish differences often minute, and on the definiteness with which we mark off and lay out the several divisions of our work. A thorough analysis and classification of the various faculties of the mind is necessary, in the first place, before we enter upon the special investigation of any one of them. Such a classification must serve as our guide-book and chart in all further inquiries.