Step 1: Understand the Doctrine of Severability.
This doctrine, derived from Article 13 of the Constitution, states that if a part of a law is found to be unconstitutional, only that offending part will be declared void, not the entire law.
The valid parts will remain in force, provided they can be separated ("severed") from the invalid parts.
Step 2: Identify the landmark case.
While the principle existed earlier, the Supreme Court comprehensively laid down the clear rules and tests for applying the Doctrine of Severability in the case of R.
M.
D.
Chamarbaugwala v.
Union of India (1957).
The court outlined the principles to determine whether the valid and invalid provisions of a statute are separable or if they are so intertwined that the whole statute must fall.