It is on the basis of the Imagination, aided by Experience and Reason, that we establish our conviction of the permanence of the simplest Laws of Nature. This I have touched on in one of my previous letters. The Memory, recalling the sight of many stones falling to the ground, comes perhaps to the aid of Attention, as a child notes a particular stone falling to the ground, and suggests to the child’s imitative nature an experimental attempt to make a stone fall to the ground. The child does it once and again, as often as he likes. Then, as a result of this unvarying experience, there springs up in the child’s mind a picture in which he sees reproduced an apparently endless vista of his sensations as to stone-falling and its antecedents, a picture not confined, like the pictures of Memory, to past time, but including future as well as past and present; and thus the childish thought leaps upwards all at once to the conception of that sublime word “always,” and dares to promulgate its first universal proposition, and attains to the definite certainty of a Law of Nature. But you say that the Imagination is “illusive.” It is; it rarely conducts us to truth without first leading us through error. Its business is to find likenesses and connections and to suggest explanations, not to point out differences, and make distinctions, and test explanations; these latter tasks are to be accomplished not by Imagination but by Reason with the aid of enlarged experience. The Imagination suggests to the child that every man is like his father, every woman like his mother; that the motion of the sea is like the motion of water in the washing basin; that the thunder is caused by the rolling of barrels or discharge of coals up above; that a clock goes on of itself for ever; and a multitude of other illusions all arising from the same healthy imaginative conviction in every young mind that “What has been will be,” and “The whole world is according to one pattern.” The conviction is based on a profound general truth, but the particular shapes which it assumes are often erroneous. It is only after a course, and sometimes a very long course, of experience and experiment, that the child, or perhaps the man, eliminates with the aid of Reason those ideas which will not work, and confirms those that will work, till the latter become at last strong and inherent and quasi-instinctive convictions. None the less, if the Imagination did not first suggest the ideas on which the Reason is to operate, we should never obtain anything worth calling knowledge.