The study of political legitimacy is divided between prescriptive and descriptive approaches. Political philosophy regards legitimacy as principled justification, sociology regards legitimacy as public support. However, all people can, and occasionally do engage in morally reasoning their political life. This paper thus submits that in studying socio‐political legitimation – the legitimacy‐making process – the philosophical ought and the sociological is can be bridged. I call this construct ‘public political thought’ (PPT), signifying the public's principled moral reasoning of politics, which need not be democratic or liberal. The paper lays PPT's foundations and identifies its ‘builders’ and ‘building blocks’. I propose that the edifice of PPT is built by moral agents constructing and construing socio‐moral order (nomization). PPT's building blocks are justificatory common beliefs (doxa) and the deliberative language of legitimation. I illustrate the merits of this groundwork through two empirical puzzles: the end of apartheid and the emergence of Québécois identity.