The political doctrine of the Commonwealth was: our state is a republic under the presidency of the King. Chancellor Jan Zamoyski summed up this doctrine when he said that Rex regnat et non gubernat ("The King reigns but does not govern").
The foundation of the Commonwealth's political system, the "Golden Liberties" (Polish: Złota Wolność, a term used from 1573 on), included:
- election of the king by all nobles wishing to participate, known as wolna elekcja (free election);;
- Sejm, the Commonwealth parliament which the king was required to hold every two yearsIn the Kingdom of Poland "Sejm" referred to the entire three-chamber parliament of Poland, comprising the lower house (Chamber of Envoys), the upper house(Senate; Polish: Senat) and the King. It was thus a three-estate parliament.;
- Pacta conventa, "agreed-to agreements" negotiated with the king-elect, including a bill of rights, binding on the king, derived from the earlier Henrician Articles.
- religious freedom guaranted by Warsaw Confederation Act 1573,
- rokosz (insurrection), the right of szlachta to form a legal rebellion against a king who violated their guaranteed freedoms;
- liberum veto (Latin), the right of an individual Sejm deputy to oppose a decision by the majority in a Sejm session; the voicing of such a "free veto" nullified all the legislation that had been passed at that session; during the crisis of the second half of the 17th century, Polish nobles could also use the liberum veto in provincial sejmiks;
- konfederacja , the right to form an organization to force through a common political aim.
This political system unusual for its time stemmed from the ascendance of the szlachta noble class over other social classes and over the political system of monarchy. In time, the szlachta accumulated enough privileges that no monarch could hope to break the szlachta's grip on power. However this grip became concentrated in a few magnate families, who these bought the votes of the minor szlachta through money and privileges. The Commonwealth's political system is difficult to fit into a simple category, but it can be tentatively described as a mixture of:
- confederation and federation, with regard to the broad autonomy of its regions. It is, however, difficult to decisively call the Commonwealth either confederation or federation, as it had some qualities of both of them;
- oligarchy, as only the szlachta—around 15% of the population—had political rights;
- democracy, since all the szlachta were equal in rights and privileges, and the Sejm could veto the king on important matters, including legislation , foreign affairs, declaration of war, and taxation (changes of existing taxes or the levying of new ones). Also, the 15% of Commonwealth population who enjoyed those political rights (the szlachta) was a substantially larger percentage than in majority European countries; note that in 1789 in France only about 1% of the population had the right to vote, and in 1867 in the United Kingdom, only about 3%.
- elective monarchy, since the monarch, elected by the szlachta, was Head of State;
- constitutional monarchy, since the monarch was bound by pacta conventa and other laws, and the szlachta could disobey any king's decrees they deemed illegal.
However since the Zebrzydowski's rokosz (1606–07) marked a substantial increase in the power of the magnates, and the transformation of szlachta democracy into magnate oligarchy. The Commonwealth's political system was vulnerable to outside interference, as Sejm deputies bribed by foreign powers might use their liberum veto to block attempted reforms. This sapped the Commonwealth and plunged it into political paralysis and anarchy for over a century, from the mid-17th century to the end of the 18th, while its neighbors stabilized their internal affairs and increased their military might.
Lessons learned in the Deluge and the Khmelnytsky (Chmielnicki) Uprising of 1648, (caused by a magnates overreach of power) taught Prince Jakob of the urgent need for reform. In this case Jakob would, with support of the minor szlachta propose a reform of the constitution:
The new constitution would look something like this, based alot on the later 3rd of May Constitution:
- abolished the liberum veto ;
- provided for a separation of powers among legislative, executive and judicial branches of government;
- established "popular sovereignty" and extended political rights to include not only the nobility but the bourgeoisie;
- increased the rights of the peasantry;
- better state control of finances and taxation
- preserved religious tolerance