We have been warned, by no one less than Plato: unless political power and philosophy are conjoined, the polis nor humanity itself will be free from trouble. This dissertation seeks to provide an argument of how this warning could be heeded in the modern polis, i.e. the democratic constitutional state.  Through reconstruction of jurisprudence of constitutional and supreme courts regarding the (un)constitutionality of constitutional amendments and constitutional laws, this dissertation proposes a sketch of an encompassing theory that clarifies what I call the core of constitutionalism. Dignity is the key concept within this theory. Without invoking natural law conceptions, the theory proposed herein – drawing on Habermas’s discourse theory, Dworkin’s conception of dignity and Murphy’s conception of constitutional coherence – rethinks the idea of constituent power, which, I argue taking as the basis the aforementioned judicial practice, is inherently circumscribed. Once it has been exercised, it becomes extinguished and transformed in the core of constitutionalism that is composed of trias: the principle of democracy, the principle of the rule of law, and the principle of fundamental (basic) rights. The core sets forth a number of criteria on the basis of which courts can reasonably come to the above judgements. In turn, the judgements analysed cast new light on the evolution and endurance of constitutional democracies. A second aim of this dissertation is to argue that the phenomenon of unconstitutional constitutional amendments can never be fully understood from the perspective of a single field of study such as constitutional theory. Constitutional unamendability is a phenomenon that should be examined concomitantly from perspective of philosophy, sociology, legal and constitutional theory as well as political theology. By establishing a conceptual link between these domains of studies, focused on the phenomenon of constitutional (un)amendability, one day down the line scholars could be ready to speak, with mutual understanding, on issues with which modern constitutional democracies struggle.