The correct answer is: "social contract and popular sovereignty".
The Enlightenment philosophers, such as Locke, Monstequieu or Rosseau, introduced ideas that challenged, and ended up derrocating, the power structures of the Old Regime. They promoted reason and the scientific method over religious dogmatism and superstititions.
The main principles developed were the following: definition of bills of citizens' rights, social contract (citizens electing political representatives to create goverments through suffrage, in opposition to the prevailing absolute monarchies), and the division of the powers of the state in order to avoid excessive power accumulation in certain sectors, and risks of authoritarism.