The application of these truths to the business of education, we shall attend to in its proper place; in the meantime we may remark, of how much importance it is, that all knowledge communicated to the young be simple, and that for some time it consist chiefly of sensible objects, and their qualities;--objects which they either know, or can have access to. Abstract subjects are not suited for children, till they can group, and classify, and compare the sensible objects with which they are already acquainted. The aim of the teacher, therefore, ought to be, strictly to follow Nature in this early stage of her operations, and to furnish food for his pupils, of the proper kind, and in proper proportions;--keeping the thinking powers constantly in healthful exercise, by giving as many ideas as the mind can reiterate without fatigue; but carefully avoiding all hurry or force, seeing that the powers of the mind are greatly weakened and injured by a multiplicity of objects, particularly when they are presented so rapidly, that the thoughts have not time to settle upon them, nor the mind to reiterate the ideas which they suggest. CHAP. VI. _On the Application of Knowledge by the Principle of Association, or Grouping._ Another principle which exhibits itself in the acquisition of knowledge by Nature's pupils, is that of "grouping," or associating objects together, after they are individually known. A child, or even an infant, who is frightened, or alarmed, or who suffers any severe injury, remembers the several circumstances, and has the place, the persons, and the things connected with the event, all associated together, and grouped into one scene or picture on the memory. These objects may have been numerous; but by the operation of this principle, they have all been apprehended, and united so powerfully with each other, that no future effort of the child can either separate or obliterate any portion of them; and so comprehensive, that the recollection of any one of the circumstances instantly recalls all the others. These groupings in the mind of a child, formed chiefly by means of the imagination, are almost wholly compounded of sensible objects; and the only necessary prerequisite for their formation appears to be a knowledge of the individual elements of which they are to be composed. If an unknown object be presented to the mind in connection with the others that are known, it is generally excluded, and the things previously known retained. For example, in the case supposed above, of an accident occurring to a child, there would be thousands of objects present, and all cognisable by the senses; but not one of all these that were unknown, that is, that had not previously undergone the process of individuation, is found to form part of the remembered group.