Sustainability as a Normative Concept in Comparative Private Law: Legal Formalisation, Doctrinal Structures, and Transnational Effects

This thesis reconstructs sustainability as a normative concept and juridical fact within comparative private law, demonstrating how it migrates from political discourse into enforceable private ordering through the interaction of legal formants – legislation, case law, doctrine, and private standard setting. Rather than seeking a univocal definition, it maps the conditions under which sustainability acquires juridical relevance across systems and sectors, showing how norm diffusion and institutional uptake generate concrete legal effects even where doctrinal qualification remains unsettled. The analysis traces a multi level trajectory from international and constitutional recognition to corporate regulation and private enforcement, with particular attention to European instruments whose obligations cascade through value chains and reconfigure contractual expectations and liability exposure. Methodologically, the thesis adopts a functional, comparative approach centred on dissociated legal formants and transnational circulation, with Europe as the primary field and the United States and China as counterpoints for divergence and functional analogy. This perspective captures the hybridisation of public and private governance through which sustainability is internalised in contracts, corporate policies, procurement, and reporting architectures. Doctrinally, the core inquiry evaluates the stabilisation of sustainability through general clauses, implied terms, and transversal principles. It interrogates proposals such as eco reasonableness and legitimate expectations, while identifying structural limits in implication techniques – including conflicts with express terms, demands of legal certainty, and judicial reticence toward open ended performance duties. The study thereby elucidates when and how sustainability can be integrated, implied, or otherwise operationalised without collapsing doctrinal boundaries or undermining party autonomy. The thesis further examines enforcement through environmental and climate litigation, greenwashing and securities claims, and the design of contractual sustainability clauses that privilege integrative interpretation, gap filling cooperation duties, and proportionate, chain adequate remedies. It extends the analysis to experimental governance – sandboxes, safe harbours, and anticipatory regimes in data, AI, and green technologies – to show how sustainability shapes institutional design in legally fluid environments. The contribution is a calibrated account of sustainability as a transnational grammar of private law: a source of normative orientation and legal effects whose force depends on systemic openness, regulatory diffusion, and disciplined interpretive practice. The thesis acknowledges countervailing tensions – certainty, justiciability, distributive burdens, and political backlash – and argues for a model of juridical integration that governs by coherence rather than overreach.