How governments are structured

Government does three distinguishable things: it makes law, it carries law out, and it interprets and applies law to disputes. Legislature, executive and judiciary correspond to these, and the reason for separating them is that combining them removes any check on abuse.

Separation is never total. Executives propose most legislation in practice, courts effectively shape law through interpretation, and legislatures conduct investigations. The realistic description is not separated powers but overlapping powers that can restrain each other.

In a presidential system the executive is elected separately and serves a fixed term, independent of the legislature. This produces a clear mandate and stability, but also the possibility of deadlock when the two branches are controlled by opposing parties.

In a parliamentary system the executive is drawn from the legislature and governs only while commanding its confidence. This makes deadlock rarer and removal easier, at the cost of less separation and, where coalitions are common, more governmental instability.

• Codified constitutions put fundamental rules in a single entrenched document, harder to change than ordinary law.
• Uncodified constitutions, as in the United Kingdom, spread those rules across statutes, court decisions and conventions.
• Entrenchment protects rights from short-term majorities but also makes correcting mistakes slow.
• Judicial review lets courts strike down laws conflicting with the constitution, which shifts real power toward judges.
• Federal systems divide power between national and regional governments; unitary systems keep it central and delegate.

First past the post awards each district to whoever gets the most votes. It tends to produce two large parties, clear single-party governments, and a strong link between a representative and a place, while wasting many votes and under-representing geographically spread support.

Proportional representation allocates seats in line with vote share. It represents minority views more accurately and usually requires coalitions, which means bargaining after the election rather than before. Neither system is neutral: the choice of rule changes which parties exist, not only which ones win.

Elections are a blunt and infrequent instrument, so systems build other checks: free press, freedom of information laws, independent audit bodies, ombudsmen, parliamentary committees and independent electoral commissions.

These depend on norms as much as on rules. A written protection is only as strong as the willingness of officials and courts to enforce it, which is why the health of institutions is assessed by behaviour over time rather than by reading the constitution alone.