Concept:
- The division of powers can be understood by asking, for any given subject, how far its effects reach.
- Subjects whose effects cross the whole country go to the centre, those confined to one state go to the state, and those that touch both are shared.
Step 1: Subjects whose effects reach the whole country.
Defence, foreign affairs, banking, communications and currency cannot work differently in different states. One army, one currency and one foreign policy are the only workable arrangement, so these form the
Union List and only the Union Government legislates on them.
Step 2: Subjects whose effects stay inside one state.
Police, trade, commerce, agriculture and irrigation depend on local soil, rainfall, crops and conditions. A single rule for the whole country would fit none of the states properly, so these form the
State List.
Step 3: Subjects that touch both levels.
Education, forest, trade unions, marriage, adoption and succession matter to the state and to the nation together. These form the
Concurrent List, on which both may legislate.
Because two laws on the same subject could clash, the Constitution settles the question in advance by giving the union law priority.
Step 4: Subjects nobody could have listed in advance.
Technology creates subjects that did not exist when the Constitution was written, such as computer software. These
residuary subjects are given to the Union Government so that no area is left without a lawmaker.
Step 5: The protection around the whole scheme.
Neither level can take powers from the other at will. Changing the division requires a two thirds majority in both Houses of Parliament and ratification by at least half the state legislatures, which keeps the federal balance secure.
Final Answer: The Constitution sorts subjects by how far their effects reach, giving national matters to the Union List, local matters to the State List, shared matters to the Concurrent List with union law prevailing, and all unlisted subjects to the Union Government.