Nova Constitutio Futuris Formam Imponere Debet, Non Praeteritis means a new law has to be prospective and not retrospective in its operation. Hence, a new statute of law has to affect the future, not the past. For instance- a new tax law cannot levy a tax on previous income, it can levy a tax on future income. This maxim implies that except in special cases the new law has to read to interfere as little as possible with already vested rights. It incorporated a particular rule of establishment which is constructive only when the words of the Act of the Parliament are vague and plain. So, if any enactment requires to be performed as retrospective it must be interpreted.
However, it is presumed that the legislature does not intend to prejudice the tendency against giving certain Statutes a retrospective operation. As a rule, new Statutes are construed as operating only in cases or facts that come into existence after the enactment. It is also settled that no Statute shall be construed to have a retrospective effect unless such enactment appears very clearly in the terms of the acts or arises by necessary and distinct implication.
The wording of the Constitution and judicial review is constructed in such a way that no existing law will be struck down as a whole but only to the extent of its inconsistency. In Keshavan Madhavan Menon v. State of Bombay AIR (1951 S.C 128), the question arose whether the fundamental rights and freedom guaranteed to each citizen has a retrospective effect or prospective effect? The court held that the language of Art. 13 did not allow retrospective operation and will not render the law void ab initio.
There are many established principles in respect of retrospective effects of statues. Such as in Amireddi Raja Gopala Rao v. Amireddi Sitharamamma – “Every statute, which takes away or impairs vested rights acquired under existing laws, or creates a new obligation or imposes a new duty, or attaches a new disability in respect of transactions already past, must be presumed to be intended not to have a retrospective effect”. “As a logical corollary of the general rule, that retrospective operation is not taken to be intended unless that intention is manifested by express words or necessary implication, there is a subordinate rule to the effect that a statute or a section in it is not to be construed to have a larger retrospective operation than its language renders necessary” (Reid v. Reid). In other words, “close attention must be paid to the language of the statutory provision for determining the scope of the retrospective intended by Parliament”- (Union of India v. Raghubir Singh)