Thomas Jefferson writing to John Adams, from Paris, 28 September 1787:
The first principle of a good government, is certainly a distribution of its powers into executive, judiciary, and legislative, and a subdivision of the latter into two or three branches. It is a good step gained, when it is proved that the English constitution, acknowledged to be better than all which have preceded it, is only better, in proportion as it has approached nearer to this distribution of powers. From this, the last step is easy, to show by a comparison of our constitutions with that of England, how much more perfect they are.
Found, entirely at random, in Memoirs, Correspondence and Miscellanies from the papers of Thomas Jefferson; ed Thomas Jefferson Randolph, 1829 Vol 2, p167 (courtesy of Project Gutenberg)