But Vico maintained that the one was continually progressing towards the other, positive law showing an increasing tendency to draw nearer to natural and rational law.
Having once derived this conception from Roman history, he was easily and indeed necessarily carried on to the next - that the positive law of all nations, throughout history, is a continual advance, keeping pace with the progress of civilization, towards the philosophic and natural law founded on 'the principles of human nature and human reason.
Its theoretical basis is the principle of egoism; while, for practically determining the particulars of duty it makes morality entirely dependent on positive law and institution.
The latter clearly distinguished between a positive law differing in different nations and a natural law based on a general and unchanging principle of human nature, and therefore obligatory upon all.
He believed, moreover, that natural law and positive law moved on almost constant and immutable parallel lines.