Q.Neha says presidential-vs-parliamentary distinction is simply about having a president or PM. Explain why this isn't always so.

Not every country organises its executive the same way. Broadly, executives fall into three types, built on two underlying principles — systems based on collective leadership, and systems based on individual leadership.

Systems based on collective leadership split further into two types. First, the parliamentary executive — the head of government is usually called the Prime Minister, who is the leader of the majority party (or coalition) in the legislature and who is accountable to that legislature. The separate head of state in such a system may be a hereditary Monarch (making it a Constitutional Monarchy, e.g., the United Kingdom or Canada) or an elected President (making it a Parliamentary Republic, e.g., India, Germany, Italy, Japan). In both cases, this head of state is a largely ceremonial executive — a formal figurehead with limited real power, while the Prime Minister and cabinet hold effective power. Second, the semi-presidential executive — the system has both a President (head of state) and a Prime Minister (head of government), but unlike a purely parliamentary system, the President here holds real, independent day-to-day powers. The Prime Minister and Council of Ministers remain responsible to the legislature. France, Russia, and Sri Lanka are examples; the President and Prime Minister in such a system may belong to the same political party, or to two different (even opposed) parties.

Systems based on individual leadership give us the third type: the presidential executive — a single President combines both the Head of State and the Head of Government roles in one office, holds real executive power, is usually directly elected by the people, and (unlike a Prime Minister) is not accountable to the legislature — the legislature cannot remove the President through a no-confidence vote. The United States, Brazil, and most Latin American countries follow this model, and the office of president in such systems tends to be very powerful, both in theory and in practice.

A useful worked example is Sri Lanka's semi-presidential system, adopted in 1978: the President is directly elected by the people for a six-year term, chooses the Prime Minister from whichever party has a majority in Parliament, and — unusually — can also remove the Prime Minister or ministers, even though those ministers must themselves be members of Parliament. The Sri Lankan President is simultaneously the elected Head of State, the Commander-in-Chief of the armed forces, and the Head of Government — combining roles that, in a parliamentary system like India's, are split between two different offices.