A legislation, be it a statutory Act or a statutory Rule or a statutory Notification, may physically consists of words printed on papers. However, conceptually it is a great deal more than an ordinary prose. There is a special peculiarity in the mode of verbal communication by a legislation. A legislation is not just a series of statements, such as one finds in a work of fiction/non fiction or even in a judgment of a court of law.

There is a technique required to draft legislation as well as to understand legislation.

Former technique is known as legislative drafting and latter one is to be found in the various principles of ‘Interpretation of Statutes'. Vis-à-vis ordinary prose, a legislation differs in its provenance, lay-out and features as also in the implication as to its meaning that arise by presumptions as to the intent of the maker thereof.

Prospective effect presumed: Of the various rules guiding how a legislation has to be interpreted, one established rule is that unless a contrary intention appears, a legislation is presumed not to be intended to have a retrospective operation. The idea behind the rule is that a current law should govern current activities. Law passed today cannot apply to the events of the past. If we do something today, we do it keeping in view the law of today and in force and not tomorrow's backward adjustment of it. Our belief in the nature of the law is founded on the bed rock that every human being is entitled to arrange his affairs by relying on the existing law and should not find that his plans have been retrospectively upset. This principle of law is known as lexprospicitnon respicit: law looks forward not backward. A retrospective legislation is contrary to the general principle that legislation by which the conduct of mankind is to be regulated when introduced for the first time to deal with future acts ought not to change the character of past transactions carried on upon the faith of the then existing law.

The obvious basis of the principle against retrospectivity is the principle of 'fairness', which must be the basis of every legal rule. Thus, legislations which modified accrued rights or which impose obligations or impose new duties or attach a new disability have to be treated as prospective unless the legislative intent is clearly to give the enactment a retrospective effect; unless the legislation is for purpose of supplying an obvious omission in a former legislation or to explain a former legislation. We need not note the cornucopia of case law available on the subject because aforesaid legal position clearly emerges from the various decisions.

Where a benefit is conferred by a legislation, the rule against a retrospective construction is different. If a legislation confers a benefit on some persons but without inflicting a corresponding detriment on some other person or on the public generally, and where to confer such benefit appears to have been the legislators object, then the presumption would be that such a legislation, giving it a purposive construction, would warrant it to be given a retrospective effect. This exactly is the justification to treat procedural provisions as retrospective. In Government of India & Ors. v. Indian Tobacco Association - 2005-TIOL-109-SC-CUS, the doctrine of fairness was held to be relevant factor to construe a statute conferring a benefit, in the context of it to be given a retrospective operation. Where a law is enacted for the benefit of community as a whole, even in the absence of a provision the statute may be held to be retrospective in nature.

In such cases, retrospectively is attached to benefit the persons in contradistinction to the provision imposing some burden or liability where the presumption attaches towards prospectivity. Thus, the rule against retrospective operation is a fundamental rule of 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. Dogmatically framed, the rule is no more than a presumption, and thus could be displaced by out weighing factors.

Under certain circumstances, a particular amendment can be treated as clarificatory or declaratory in nature. Such statutory provisions are labelled as "declaratory statutes". The circumstances under which a provision can be termed as "declaratory statutes" is explained by Justice G.P. Singh Principles of Statutory Interpretation, 13th Edition 2012 published by Lexis Nexis Butterworths Wadhwa, Nagpur in the following manner:

Declaratory statutes

The presumption against retrospective operation is not applicable to declaratory statutes.

"For modern purposes a declaratory Act may be defined as an Act to remove doubts existing as to the common law, or the meaning or effect of any statute. Such Acts are usually held to be retrospective. The usual reason for passing a declaratory Act is to set aside what Parliament deems to have been a judicial error, whether in the statement of the common law or in the interpretation of statutes. Usually, if not invariably, such an Act contains a preamble, and also the word 'declared' as well as the word 'enacted'. But the use of the words 'it is declared' is not conclusive that the Act is declaratory for these words may, at times, be used to introduced new rules of law and the Act in the latter case will only be amending the law and will not necessarily be retrospective. In determining, therefore, the nature of the Act, regard must be had to the substance rather than to the form. If a new Act is 'to explain' an earlier Act, it would be without object unless construed retrospective. An explanatory Act is generally passed to supply an obvious omission or to clear up doubts as to the meaning of the previous Act. It is well settled that if a statute is curative or merely declaratory of the previous law retrospective operation is generally intended. The language 'shall be deemed always to have meant' is declaratory, and is in plain terms retrospective. In the absence of clear words indicating that the amending Act is declaratory, it would not be so construed when the pre-amended provision was clear and unambiguous. An amending Act may be purely clarificatory to clear a meaning of a provision of the principal Act which was already implicit. A clarificatory amendment of this nature will have retrospective effect and, therefore, if the principal Act was existing law which the Constitution came into force, the amending Act also will be part of the existing law."

Assessment creates a vested right and an assessee cannot be subjected to reassessment unless a provision to that effect inserted by amendment is either expressly or by necessary implication retrospective.

Now it is a well settled rule of interpretation hallowed by time and sanctified by judicial decisions that, unless the terms of a statute expressly so provide or necessarily require it, retrospective operation should not be given to a statute so as to take away or impair an existing right or create a new obligation or impose a new liability otherwise than as regards matters of procedure.

The general rule as stated by Halsbury in Vol. 36 of the Laws of England (3rd Edn.) and reiterated in several decisions of the Supreme Court as well as English courts is that all statutes other than those which are merely declaratory or which relate only to matters of procedure or of evidence are prima facie prospectively and retrospective operation should not be given to a statute so as to affect, alter or destroy an existing right or create a new liability or obligation 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.

From a recent judgement of the Supreme Court of India reported in 2014-TIOL-78-SC-IT-CB

The Babus engaged in drafting laws can help in avoiding useless litigation, if they understand these concepts.