Public choice applies to political actors the same assumptions economics applies to everyone else. Voters, legislators, regulators and bureaucrats pursue their own interests and not an abstract public good, and political outcomes should be explained accordingly. James Buchanan called the program politics without romance, a phrase that captures both its analytical discipline and the objection it attracts.
Buchanan and Gordon Tullock's The Calculus of Consent (1962) founded the field, analyzing constitutional rules as the outcome of bargaining among people who do not know how they will later be placed. A series of durable concepts came out of it. Rent-seeking is the expenditure of real resources to capture transfers instead of creating value. Rational ignorance is the voter's reasonable decision not to research questions their vote will not determine. Concentrated benefits and diffuse costs explains why small organized groups routinely defeat larger unorganized ones. Regulatory capture followed. Mancur Olson on collective action and Arrow's impossibility theorem sit alongside these as foundations.
Buchanan's distinctive move was constitutional. Since he expected self-interest at every level, he located the remedy in rules rather than in better officials: rules chosen behind enough uncertainty about one's own future position that they have to be general. The argument earned the Nobel in 1986 and reads as a Rawlsian device turned to different ends.
Two serious objections follow it. Empirically, the pure self-interest assumption predicts turnout and much bureaucratic behavior badly, and the field has had to soften it. Politically, critics argue that an analysis finding democratic politics inherently corrupt supplies a rationale for insulating decisions from democratic control, a charge pressed polemically in Nancy MacLean's Democracy in Chains and disputed in detail by scholars of Buchanan's work. Elinor Ostrom's Bloomington school stands as the empirical counterweight from inside the same broad camp, showing communities solving collective-action problems the theory predicted they could not.