This paper focuses on the question about the normative or descriptive character of constitutional theory. A constitutional study is normativist when we ask what the roles of a constitution ought to be, we choose between different institutions and processes, and we evaluate how well they perform for guaranteeing (specific) values. Conversely, a descriptivist view rejects universalism and idealism in constitutional theory and looks for the existing constitutional practices. By means of British constitutional debates, I argue that both normativist and descriptivist approaches are necessary, but neither can satisfy the constitutional theory’s demands by itself. First, constitutional design is called to act in the real world, considering the circumstances of political societies where institutions are applied. Second, it is highly contested to say that a pure descriptive theory is possible. Then, a reconciliation in this divide is advisable. I present some ideas on how to conceive it.