The doctrine of casus omissus outlines the circumstances where a court can supply a clearly unintended omission by the legislature in drafting a particular provision. This issue arises quite frequently and in varying circumstances. There have been several recent and conflicting decisions on the point.
To begin with English law, casus omissus is perhaps better known as the doctrine that provoked Lord Simonds’ famous prescription against the judiciary’s “naked usurpation of the legislative function under the thin disguise of interpretation” (Magor & St. Mellons Rural District Council v. Newport,  2 All ER 839). This observation was provoked by two decisions of Lord Denning that refused to follow the then settled rule that a court could not extend the language of a statutory provision to fill a casus omissus even if it was obviously unintended and resulted in severe anomalies in the Act (Seaford Court Estates v. Asher and Magor & St. Mellons Rural District Council). Consequently, it was held in decisions leading upto to Wentworth Securities v. Jones that a casus omissus could not be supplied (Wentworth Securities v. Jones,  AC 74). In Wentworth, Lord Diplock revived the doctrine by formulating three conditions for its exercise – precise determination of mischief, apparent and inadvertent omission by the draftsman, and the ability to state with certainty the language the draftsman would have employed. In 2000, the House of Lords effectively approved these conditions, in the landmark case on the point – Inco Europe v. First Choice Distribution (Inco Europe v. First Choice Distribution,  2 All ER 109). The House of Lords also formulated exceptions to the rule, some of which are that the power will not be exercised when the alteration proposed is “far-reaching”, or when the legislation in question requires strict construction as a matter of law.
In 2004, Professor Auchie argued (25 STATUTE LAW REVIEW 40) that Inco Europe is not just inconsistent with precedent, but also “entirely unjustified”, for it left too much to the courts with a consequent “danger of mistake”. In an article I published recently (30 STATUTE LAW REVIEW 73) I have suggested that this danger is somewhat overstated. The doctrine, after the Wentworth conditions and the Inco exceptions are satisfied, is so limited in scope that it is capable of being resorted only in the rarest of circumstances. I argued that “the danger of mistake” in those circumstances is outweighed by the possible benefit of giving effect to what is plainly the legislature’s intent. A case in point is s. 27 of the Indian Evidence Act (perhaps the clearest example of an unintended casus omissus).
On casus omissus itself, Indian law is difficult to ascertain, as there are parallel lines of authority. In a 1952 decision (Hira Devi v. District Board, Shahjahanapur,  1 SCR 122) that is quite similar to Inco, the Supreme Court followed Lord Simonds’ approach. Several other cases support this view (P.K. Unni v. Nirmala Industries, (1990) 2 SCC 378; Baliram Waman Hiray v. Justice B. Lentin, (1988) 4 SCC 419). On the other hand, the Court in Dadi Jagannatha (Dadi Jagannadham v. Jammulu, (2001) 7 SCC 71) (overruling Nirmala Industries) and SR Bommai cautiously took the opposite view. However, the most authoritative precedent in support of the broader conception of casus omissus, OS Singh (OS Singh v. Union of India, (1996) 7 SCC 37) is somewhat unpersuasive, as it appears to have misread certain cases that it relies on for its conclusion. These lines of authority cannot be easily reconciled, and if the Supreme Court is to resolve the matter, it is likely to consider the matter afresh.
One recent development that is of great interest in this context is a decision of Justice Katju in Rajbir Singh Dalal v. Chauhari Devi Lal University, (2008) 9 SCC 284. In this decision, Justice Katju has continued his strong criticism of the use of traditional principles of statutory interpretation. He has suggested that casus omissus, known as “adhyahara” in the Mimamsa school of interpretation permits courts to add words to a legal text. The Court has further observed that this is “superior to Maxwell’s principles in this respect” since Maxwell “does not go into any further detail and does not mention sub-categories coming under the general category of casus omissus”. This decision may require reconsideration, and in any event has to be read in light of another recent judgment that reaffirms the narrow view of casus omissus – Union of India v. Dharmendra Textile Processors, (2008) 13 SCALE 233.
It is perhaps time for the Supreme Court to settle the exact scope of the doctrine.