This thesis argues that 'democracy' can better be understood in terms of a conceptual diarchy of 'isonomia' (equal political rights) and 'isegoria' (equal speech rights), rather than the conventional diarchy of 'will' and 'opinion' that originated in the era of absolute monarchy. As the proposed diarchy has its origin in classical Greece, the thesis starts with a brief overview of the institutional changes in sixth-, fifth- and fourth-century Athenian democracy that implemented the distinction in different ways, and examines some of its dysfunctions. The particular aspect of Athenian democracy under focus is sortition - the random selection of citizens for public office - viewed in antiquity as democratic, whereas election was viewed as an aristocratic or oligarchic selection mechanism. The thesis takes issue with Bernard Manin's claim that the 'triumph of election' was on account of the natural right theory of consent, arguing that sortition-based proxy representation is a better way of indicating (hypothetical) consent than preference election. The thesis then seeks to clarify the concept(s) of representation - essential to the implementation of the democratic diarchy in modern large-scale societies - and to study how the diarchy has been reincarnated in modern representative democracies, along with an examination of the pathologies thereof. Consideration is given as to what the deliberative style of assemblies selected by lot should be, alongside evaluation of the epistemic potential of cognitive diversity and the 'wisdom of crowds'. Given the need for both isonomia and isegoria to assume a representative form in large modern states, Michael Saward's Representative Claim is adopted as a theoretical model to extend the reach of political representation beyond elections. The thesis concludes with tentative proposals as to how the fourth-century reforms (delegation of the final lawmaking decision to randomly-selected nomothetic courts) might be used as a template for modern institutions to resolve some of the problems of mass democracy.