Why is the Constitution of India called as a living document?

The Constitution of India is called a living document because of it embodies a unique synthesis of flexibility and rigidity. The fact that the Constitution can be amended according to the needs of the time makes it a dynamic document. 

Constitution: A Living Document 

1. Amendment of the Constitution: Constitution must be able to address contemporary challenges. The state should be able to amend the Constitution from time to time.
   The Constitution of India provides for its amendment under Article 368-
   A) Special majority of the Parliament: Some provisions of the Constitution can only be amended by the Special Majority of the Parliament, i.e., two-third of the members of each House present and voting and a majority (that is, more than 50 percent) of the total membership of the House. The provisions which can be amended this way include Fundamental Rights, Directive Principles of State policy and all the provisions not included in any other category.
   B) Special Majority of the Parliament and ratification by half the states (by simple majority): Various provisions are included in this category such as Election of the President, 7th Schedule and so on.
   C) Simple Majority of the Parliament: This category is outside the scope of Article 368. It includes provisions such as establishment or admission of new states, abolition of Legislative Council of the states and so on. 
2. Rigidity of the Constitution: The Constitution makers made sure that the essential nature of the Constitution could not be altered. It thrives to safeguard the rights and liberties of the citizens. It imposes restrictions on the extent of power of the state. These safeguards can only be amended by a special majority of the Parliament. 
3. Role of Judiciary: Judiciary has played an important role in not only saving the essence of the Constitution but also in its evolution.
   A) Basic structure Doctrine: Propounded in the famous Keshavnanda Bharati Case, 1973 it restricts the Parliament from altering the essential features of the Constitution or what the Supreme Court termed as the Basic Structure. Basic structure includes various Constitutional ideals such as secularism, rule of law, federalism etc.
   B) Transformative nature of the Constitution: The courts, at various point of time, have brought transformative changes through a broad reading of our Constitution. Courts have regularly included various rights under the existing Fundamental Rights to suit the changing times. For example, Supreme Court in its landmark judgment in Justice Puttaswamy Case recognised Right to Privacy as a part of Fundamental Rights under Article 21. 

Therefore, the Constitution of India is not a frozen or static document but a living one. It keeps evolving not only to suit the needs of the society but also to bring transformation.