390. The ground of the proofs that establish this Science is the universal language of the universal law of the gentes which has been observed in this great city of mankind. With the language of this law we can explain the mode of the birth of the parts that comprise the entire system of the nature of nations, for science consists solely in cognition of the mode; we can exhibit the times of the birth of the first parts of each kind [of nature], for it is the distinguishing mark of a science that it should reach those origins beyond which it is utterly foolish curiosity to seek others earlier; through these same times and modes of birth we can discover the eternal properties through which alone it is possible to ascertain that their birth or nature was thus and not otherwise; and [we can reveal how], from their first beginnings, they proceeded through an uninterrupted, i.e. continuous, succession of things, in accordance with the natural progress of human ideas. This is the principal reason why, in the ‘Idea of the Work’, we conceived the present book in accordance with the expression leges aeternas [‘the eternal laws’] that the philosophers use to name the parts of law that we have treated here. Moreover, on the basis of the foregoing meditations, this work brings mythologies, which are histories of facts, into agreement with etymologies, which provide a science of the origin of things.