S.P. Gupta v. President of India, AIR 1982 SC 149: (1981) Supp 1 SCC 87
1. Where the language of a statute is clear and unambiguous, there is no room for the application either of the doctrine of casus omissus or of pressing into service external aid, for in such a case the words used by the Constitution or the statute speak for themselves and it is not the function of the Court to add words or expressions merely to suit what the Courts think is the questioned intention of the legislature.
2. Where, however the words or expressions used in constitutional or statutory provision are shrouded in mystery clouded with ambiguity and are unclear and unintelligible so that the dominant object and spirit of the legislature cannot be spelt out from the language, external aids in the nature of parliamentary debates, immediately preceding the passing of the statute, the report of the Select Committees or its Chairman, the Statement of Objects and Reasons of the statute, if any, or any statement made by the sponsor of the statute which is in close proximity to the actual introduction or insertion of the statutory provision so as to become, as it were, a result of the statement made, can be pressed into service in order to ascertain the real purport, intent and will of the legislature to make the constitutional provision workable. We might make it clear that such aids may neither be decisive nor conclusive but they would certainly assist the Courts in interpreting the statute in order to determine the avowed object of the Act or the Constitution as the case may be.
3. Except in the aforesaid cases, a mere speech of any member made on the floor of the House during the course of a parliamentary or legislative debate would not be admissible at all because the views expressed by the speaker may be his individual views which may or may not be accepted by the majority of the members present in the House.
4. Legislative history of a constitutional provision though not directly germane for the purpose of construing a statute may, however, be used in exceptional cases to denote the beginning of the legislative process which results in the logical end and the finale of the statutory provision but in no case can the legislative history take the place of or be a substitute for an interpretation which is in direct contravention of the statutory provision concerned.
5. Where the scheme of a statute clearly shows that certain words or phrases were deliberately omitted by the legislature for a particular purpose or motive, it is not open to the Court to add those words either by conforming to the supposed intention of the legislature or because the insertion or the omission suits the ideology of the Judges deciding the case. Such a course of action would amount not to interpretation but to interpolation of the statutory or constitutional provisions, as the case may be and is against all the well-established canons of interpretation of statutes.
Source: M A Rashid