Alternative Digital Platforms and the Renewal of the Public Sphere: Decidim and the Democratic Governance of Participatory Infrastructures

The objective of this article is to examine how alternative digital platforms can be designed and governed as public-interest infrastructures capable of supporting democratic deliberation in the contemporary digital public sphere. Drawing on deliberative democratic theory, the article develops a normative framework for evaluating participatory digital infrastructures and applies it to a qualitative, theory-driven case study of Decidim, an open-source participatory platform originally developed by the Barcelona City Council. Methodologically, the study combines normative analysis with qualitative documentary analysis of official platform documentation, peer-reviewed academic literature, and the institutional and technical features of the platform. The analysis shows that Decidim operationalises key deliberative principles—such as inclusion, publicity, reason-giving, transparency, traceability, and participatory governance—through its institutional design, governance model, and deliberative affordances. The findings demonstrate that algorithmic systems and digital infrastructures are not inherently incompatible with democratic values, but can be intentionally engineered to support public deliberation and democratic will-formation. The article concludes that the reconstruction of participatory digital infrastructures as public goods constitutes a democratic imperative, requiring sustained institutional commitment, political will, and a reconceptualisation of platform design as a domain of democratic governance.