Duhaime's Law Dictionary

Nova Constitutio Futuris Formam Imponere Debet, Non Praeteritis Definition:

Latin: a new law ought to be construed to interfere as little as possible with vested rights.

Edward Coke wrote:

"This (Statute of Gloucester) extendeth to alienations made after the statute, and not before, for it is a rule and law of parliament that regularly nova constitutio futuris formam imponere debet, non praeteritis."

In Gardner v. Lucas et al., Justice Blackburn wrote:

"Now the general rule, not merely of England and Scotland, but, I believe, of every civilized nation, is expressed in the maxim, “Nova constitutio futuris formam imponere debet non praeteritis” — prima facie, any new law that is made affects future transactions, not past ones."

In Reid v Reid, Justice Bowen wrote:

"Now the particular rule of construction which has been referred to, but which is valuable only when the words of an Act of Parliament are not plain, is embodied in the well-known trite maxim omnis nova constitutio futuris formam imponere debet non praeteritis, that is, that except in special cases the new law ought to be con­strued so as to interfere as little as possible with vested rights. It seems to me that even in construing an Act which is to a certain extent retrospective, and in constru­ing a section which is to a certain extent retrospective, we ought nevertheless to bear in mind that maxim as applicable whenever we reach the line at which the words of the section cease to be plain. That is a neces­sary and logical corollary of the general proposition that you ought not to give a large retrospective power to a section, even in an Act which is to some extent intended to be retrospective, than you can plainly see the Legisla­ture meant."

The often referred-to textbook on the interpretation of statutes, Maxwell, refers to nova constitutio maxim as follows:

"Upon the presumption that the legislature does not intend what is unjust rests the leaning against giving certain statutes a retrospective operation. Nova constitutio futuris formam imponere debet, non praeteritis. They are construed as operating only in cases or on facts which come into existence after the statutes were passed unless a retrospective effect be clearly intended. It is a fundamental rule of English law that no statute shall be construed to have a retrospective operation unless such a construction appears very clearly in the terms of the Act, or arises by necessary and distinct implication.

"Perhaps no rule of construction is more firmly established than this, that a retrospective operation is not to be given to a statute so as to impair an existing right or obligation, otherwise than as regards matter of procedure, unless that effect cannot be avoided without doing violence to the language of the enactment. If the enactment is expressed in language which is fairly capable of either interpretation, it ought to be construed as prospective only." But if the language is plainly retrospective it must be so interpreted."

Finally, consider these words of Canada's Supreme Cpourt Justice Duff in:

"The well known passage may be recalled in which Lord Coke (2 Inst. 292) lays it down that it is a rule and law of Parliament that regularly nova constitutio futuris formant imponere debet non praeteritis, and the rule that statutory enactments generally are to be regarded as intended only to regulate the future conduct of persons is, as Parke B. said in Moon v. Durden,2 in 1848, deeply founded in good sense and strict justice because speaking generally it would not only be widely inconvenient but a flagrant violation of natural justice to deprive people of rights acquired by transactions perfectly valid and regular according to the law of the time."


  • Gardner v. Lucas et al., [1878] 3 A.C. 582
  • Maxwell on Interpretation of Statutes, 11th ed. (1962)
  • NOTE 1: 2 Edward Coke, Institutes of the Law of England 360a
  • NOTE 2: Moon v Durden [1848] 2 Ex. 22
  • Reid v Reid, 31 Ch. D. 402 (1886) at page 408.

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