Article 366 is a crucial provision of the Indian Constitution, located in Part XIX (Miscellaneous), which functions as a comprehensive constitutional glossary. It was included by the framers to ensure uniform interpretation and prevent ambiguity of key terms used throughout the Constitution. By codifying these definitions, the article ensures that the judiciary, legislature, and executive apply a consistent understanding of crucial concepts.
The article works by assigning specific meanings to over 30 expressions, unless the context of a particular article requires otherwise. For instance, Article 366(1) defines "agricultural income" as having the same meaning as in the laws relating to Indian income-tax. Crucially, Article 366(24) defines "Scheduled Castes" as those communities specified under Article 341, and Article 366(25) defines "Scheduled Tribes" as those specified under Article 342. These definitions form the constitutional basis for social justice policies and affirmative action.
Article 366 connects directly to the taxation framework and has been significantly amended to reflect economic changes. The 46th Constitutional Amendment Act, 1982, inserted Article 366(29A), which expanded the definition of "tax on the sale or purchase of goods" to include transactions like works contracts and hire purchase, a change made after the Supreme Court's ruling in State of Madras v. Gannon Dunkerley & Co. (1958). More recently, the 102nd Constitutional Amendment Act, 2018, introduced Article 366(26C) to define "socially and educationally backward classes". Furthermore, the definition of "Ruler" under Article 366(22) was modified by the 26th Constitutional Amendment Act, 1971, which ended the recognition of princely rulers and their privileges. The Supreme Court has frequently referred to these definitions, such as in Keshavananda Bharati v. State of Kerala (1973), to interpret constitutional provisions.