“It is a principle in the English law,” says Chief Justice Kent, in the case last cited, “as ancient as the law itself, that a statute, even of its omnipotent Parliament, is not to have a retrospective effect.  ’Nova constitutio futuris formam imponere debet, et non praeteritis.’[39] The maxim in Bracton was taken from the civil law, for we find in that system the same principle, expressed substantially in the same words, that the lawgiver cannot alter his mind to the prejudice of a vested right.  ’Nemo potest mutare concilium suum in alterius injuriam.’[40] This maxim of Papinian is general in its terms, but Dr. Taylor[41] applies it directly as a restriction upon the lawgiver, and a declaration in the Code leaves no doubt as to the sense of the civil law.  ’Leges et constitutiones futuris certum est dare formam negotiis, non ad facta praeterita revocari, nisi nominatim, et de praeterito tempore, et adhuc pendentibus negotiis cautum sit.’[42] This passage, according to the best interpretation of the civilians, relates not merely to future suits, but to future, as contradistinguished from past, contracts and vested rights.[43] It is indeed admitted that the prince may enact a retrospective law, provided it be done expressly; for the will of the prince under the despotism of the Roman emperors was paramount to every obligation.  Great latitude was anciently allowed to legislative expositions of statutes; for the separation of the judicial from the legislative power was not then distinctly known or prescribed.  The prince was in the habit of interpreting his own laws for particular occasions.  This was called the ‘Interlocutio Principis’; and this, according to Huber’s definition, was, ’quando principes inter partes loquuntur et jus dicunt.’[44] No correct civilian, and especially no proud admirer of the ancient republic (if any such then existed), could have reflected on this interference with private rights and pending suits without disgust and indignation; and we are rather surprised to find that, under the violent and arbitrary genius of the Roman government, the principle before us should have been acknowledged and obeyed to the extent in which we find it.  The fact shows that it must be founded in the clearest justice.  Our case is happily very different from that of the subjects of Justinian.  With us the power of the lawgiver is limited and defined; the judicial is regarded as a distinct, independent power; private rights are better understood and more exalted in public estimation, as well as secured by provisions dictated by the spirit of freedom, and unknown to the civil law.  Our constitutions do not admit the power assumed by the Roman prince, and the principle we are considering is now to be regarded as sacred.”

These acts infringe also the thirty-seventh article of the constitution of New Hampshire; which says, that the powers of government shall be kept separate.  By these acts, the legislature assumes to exercise a judicial power.  It declares a forfeiture, and resumes franchises, once granted, without trial or hearing.