Nature, as we have seen, has rendered it imperative that the act of reiteration should be performed upon every idea before it can have an entrance into the mind, or be retained by the memory; but as the individual cannot reiterate, or think over, all the ideas suggested to him by the innumerable objects of sensation with which he is surrounded, it next becomes a matter of importance to ascertain the means employed by Nature for enabling her pupils to receive and retain the greatest number of ideas, so that they shall ever afterwards remain at the command of the will. This she accomplishes by the operation of the three other principles to which we have adverted; namely, "Individuation," or "Abstraction," "Grouping," or "Association," and "Classification," or "Analysis."--We shall in this chapter attend to the principle of "Individuation," and endeavour to trace its nature and uses in the acquisition of knowledge by the young. The first thing in an infant that will be remarked by a close observer of Nature is, that while adding to its knowledge by observation, it always confines its attention to one thing at a time, till it has examined it. Before the period when this principle becomes conspicuous in an infant, the eye, and the other senses are in a great measure inactive, so far as the mind is concerned; and the first indication of the senses really ministering to the mind is the eye chusing an object, and the infant examining that object by itself, without allowing its attention to be distracted by any thing else.