Many other circumstances might be mentioned, which conspire to prove that neither of the great works of which I have spoken, has superseded the necessity of a new attempt to lay before the public a System of the Law of Nations. The language of science is so completely changed since both these works were written, that whoever was now to employ their terms in his moral reasonings would be almost unintelligible to some of his hearers or readers; and to some among them too who are neither ill qualified nor ill disposed to study such subjects with considerable advantage to themselves. The learned indeed well know how little novelty or variety is to be found in scientific disputes. The same truths and the same errors have been repeated from age to age, with little variation but in the language; and novelty of expression is often mistaken by the ignorant for substantial discovery. Perhaps too very nearly the same portion of genius and judgment has been exerted in most of the various forms under which science has been cultivated at different periods of history. The superiority of those writers who continue to be read, perhaps often consists chiefly in taste, in prudence, in a happy choice of subject, in a favourable moment, in an agreeable style, in the good fortune of a prevalent language, or in other advantages which are either accidental, or are the result rather of the secondary than of the highest faculties of the mind.--But these reflections, while they moderate the pride of invention, and dispel the extravagant conceit of superior illumination, yet serve to prove the use, and indeed the necessity, of composing, from time to time, new systems of science adapted to the opinions and language of each succeeding period. Every age must be taught in its own language. If a man were now to begin a discourse on ethics with an account of the "_moral entities_" of Puffendorff,[12] he would speak an unknown tongue.