In these several departments of our mental constitution, and in the principles or laws by which they are carried on, we have the great thoroughfare,--the highway of education,--marked out, inclosed, and levelled by Nature herself. Hitherto, in our examination of the several processes in which we find her engaged, we have endeavoured strictly to confine ourselves to the great general principles which she exhibits in forwarding and perfecting them. We have not touched as yet on the methods by which, in our schools, they may be successfully imitated; nor have we made any enquiry into the particular truths or subjects which ought there to be taught. These matters belong to another part of this Treatise, and will be considered by themselves. And it is only necessary here to observe, that as it is the _use_ of knowledge chiefly which Nature labours to attain, it is therefore _useful knowledge_ which she requires to be taught. This is a principle so prominently held forth by Nature, and so repeatedly indicated and enforced, that in the school it ought never for an hour to be lost sight of. The whole business of the seminary must be practical; and the knowledge communicated must be useful, and such as can be put to use. If this rule be attended to, the knowledge communicated will be valuable and permanent;--but if it be neglected, the pretended communications will soon melt from the memory, and the previous labours of both teacher and pupil will be in a great measure lost. The existence of these several principles in education has been ascertained by long experience and slow degrees;--and the accuracy of the views which we have taken of them, has been rigorously and repeatedly tested. No pains has been spared in projecting and conducting such experiments as appeared necessary for the purpose; and it has been by experience and experiment alone that their efficiency has been established. Many of these experiments were conducted in public,--some of them have for years been in circulation,--and the decisiveness of their results has never been questioned. The several principles in education which it was the object of these experiments to ascertain, are here for the first time, collected and exhibited in their natural order; and they are now presented to the friends of education with some degree of confidence. Judging historically, however, from the experience of others in breaking up new ground in the sciences, there is good reason to believe, that the present Treatise goes but a short way in establishing the science of education. There is yet much to be done; and others, no doubt, will follow to complete it. But if confidence is to be placed in history, it appears evident, that they must follow in the same course, if ever they are to succeed. Nature is our only instructress; and however much she may have hitherto been neglected, it is only by following her leadings with a child-like docility, that improvement is ever to be expected.