A Doctrine is a principle, theory, or position that is usually applied and upheld by Courts of Law. See a Doctrine can either be a rule, theory or tent of law. In Indian Constitutional law, there are different judicial doctrines that develop over time as per the interpretation given by the judiciary. Some of the important judicial doctrines are discussed here.

DOCTRINE OF BASIC STRUCTURE:

• The origins of this basic structure are found in the German Constitution, which after the Nazi regime, was amended to protect some basic laws.

1. In Kesavananda Bharati case 1973, the Supreme Court of India held for the first time that the parliament has the power to amend any part of the constitution but it cannot alter the "basic structure of the constitution". 
2. It was reaffirmed by the Indira Nehru Gandhi vs Raj Narain case (1975).The SC struck down the 39th Amendment Act as it was against the principle of separation of powers. It placed the disputes relating to the president, Vice President, Prime Minister and Speaker of Lok Sabha beyond the jurisdiction of all Courts. 

1. One organ should not form part of the other 2 organ (Judiciary cannot be a part with executive and legislature).
2. One organ should not interfere in working of the other organ (Executive cannot interfere in legislative work).
3. One organ should not exercise the function of the other organ. (Legislature cannot perform duties of judiciary).
4. Article-50 of the Directive Principles of the State Policy (DPSP) puts an obligation over the state to separate the judiciary from executive. This article says,

1. In Ram Jawaya v. State of Punjab the SC held that the Doctrine of Separation of Power was not fully accepted in India.
2. In Indira Nehru Gandhi v. Raj Narain (1975), the SC held that the separation of powers is a part of the basic structure of the Constitution. None of the three separate organs of the Republic can take over the functions assigned to the other.

• The origin of this doctrine lies in Canada and in India it came to be adopted in the pre-independence period, under the Government of India Act, 1935. This Doctrine is firmly supported by Article 246 of the Constitution and the Seventh Schedule.

1. In State of Bombay Vs. F.N. Balsara, was a case in which Bombay Prohibition Act was challenged on the grounds that the prohibition of liquor on the borders was a matter of Central Government. The act was held valid by the court, it fell under the State list though it was impacting the liquor.
2. Another important case for this Doctrine in Prafulla Kumar Mukherjee v. Bank of Khulna. 

DOCTRINE OF SEVERABILITY:

It is also known as "Doctrine of Separability" and protects the fundamental rights of the citizens. As per clause (1) of the Article 13 of the Constitution, if any of the laws enforced in India are inconsistent with the provisions of fundamental rights, they shall be made void. 

The whole law/act would not be held invalid, but only the provisions which are not in consistency with the Fundamental Rights. According to this Doctrine, if there is any offending part in the statute, then the offending part can be declared as void, not the entire statute and the valid part can be kept. 

If the valid and invalid part are so closely mixed up with each other that it cannot be separated then the whole law or act will be held invalid.

• This Doctrine found its roots in England in the case of Nordenfelt v. Maxim Guns and Ammunition Company Ltd., here the issue was related to a Trade clause. Here the disputed clause was severable; and hence only a part of it become void. In this case, however, it was not exactly the doctrine of severability; it was "doctrine of blue pencil".

1. In the case of RMDC vs. UOI, SC stated that doctrine of severability is a matter of substance and not of form.
2. In A.K. Gopalan v. State of Madras (1950), the SC held that in case of inconsistency to the Constitution, only the disputed provision of the Act will be void and not the whole of it. The Court found that Section 14 of the Preventive Detention Act to be violative of Article 14 of the Constitution. Hence, the Section 14 of the Act was severed and held void, while the other provisions remain to be valid within the Statute.
3. In State of Bombay v. F.N. Balsara(1951), the disputed statute here was Bombay Prohibition Act, where the unconstitutional provision was held void and inoperative while the other part was not damaged and the Statue was stille be remaining in the force.

1. The first case in which this doctrine was applied was Bhikaji vs. State of Madhya Pradesh(It was applied to pre-constitutional laws).  
2. The extension to the post-constitutional law was stated in the case of DulareLodh vs ADJ Kanpur.