In the minor arts of life, it is obvious that general principles cannot be laid down without some theoretical study; and that the application of these rules to special cases is not to be entirely left to the untaught instinct of the artisan. And can it be otherwise with the art of Social Life, so far harder and more important than any other, and in which, from its principles being less simple and less precise, a special explanation of them in each case is even more necessary? However perfect the demonstration of social principles may become, it must not be supposed that knowledge of Positive doctrine, even when it has been taught in the most efficient way, will dispense with the necessity of frequently appealing to the philosopher for advice in questions of practical life, whether private or public. And this necessity of an interpreter to intervene occasionally between the principle and its application, is even more evident from the moral than it is from the intellectual aspect. Certain as it is that no one will be so well acquainted with the true character of the doctrine as the philosopher who teaches it, it is even more certain that none is so likely as himself to possess the moral qualifications of purity, of exalted aims, and of freedom from party spirit, without which his counsels could have but little weight in reforming individual or social conduct. It is principally through his agency that we may hope in most cases to bring about that reaction of All upon Each, which, as we have seen, is of such indispensable importance to practical morality. Philosophers are not indeed the principal source of Public Opinion, as intellectual pride so often leads them to believe. Public Opinion proceeds essentially from the free voice and spontaneous co-operation of the people. But in order that the full weight of their unanimous judgment may be felt, it must be announced by some recognized organ. There are, no doubt, rare cases where the direct expression of popular feeling is enough, but these are quite exceptional. Thus working men and philosophers are mutually necessary, not merely in the creation of Public Opinion, but also in most cases in the manifestation of it. Without the first, the doctrine, however well established, would not have sufficient force. Without the second, it would usually be too incoherent to overcome those obstacles in the constitution of man and of society, which make it so difficult to bring practical life under the influence of fixed principles.