The _first_ is the act of "Reiteration," of which we have already spoken, as the chief instrument in cultivating the powers of the mind, and without which, we shall also find, there can be no acquisition of knowledge. The _second_ is the principle of "Individuation," by which Nature communicates the knowledge of single ideas, or single objects, by constraining the child to concentrate the powers of its mind upon one object, or idea, till that object or idea is familiar, or, at least, known. The _third_ is the common principle of "Grouping, or Association," and appears to depend, in some degree, on the imaginative powers, by which a child begins to associate objects or truths together, after they have become individually familiar; so that any one of them, when afterwards presented to the mind, enables the pupil at a glance, to command all the others which were originally associated with it. The _fourth_ is the principle of "Classification, or Analysing," by which the mind distributes objects or truths according to their nature,--puts every truth or idea, as it is received, into its proper place, and among objects or ideas of a similar kind. This classification of objects is not, as in the principle of grouping, regulated according to their accidental relation to each other, by which the canary and the cage in which it is confined would be classed together; but according to their nature and character, by which the canary would be classified with birds, and the cage among other articles of household furniture. All knowledge, so far as we are aware, appears to be communicated and retained for use, by means of these four principles; and we shall now proceed to examine the mode in which each of them is employed by Nature for that purpose. FOOTNOTES: [2] Note A. CHAP. IV. _On Nature's Method of communicating Knowledge to the Young by the Principle of Reiteration._ We have, in a former chapter, endeavoured to describe that particular act of the mind which generally follows simple perception, and by which an idea, when presented to it, is made the subject of _active thought_, or is "_reiterated_" again to itself. We have found upon good evidence, that it is by this process, whether simple or complex, that the powers of the mind are cultivated; and we now proceed to shew, that it is by the same act, and by it alone, that any portion of knowledge is ever communicated.[3] No truth, or idea of any kind, can make an effective entrance into the mind, or can find a permanent lodgement in the memory, so as to become "knowledge," until it has successfully undergone this process.