The social phenomenon of rare diseases: a logical-modal analysis.

This paper explores the social phenomenon of rare diseases through a logical-modal analysis. Although rare diseases originate within a biomedical framework and are increasingly recognised by institutional and empirical literature as issues of equity, inclusion, care and participation, this recognition has not usually been formalised in Durkheimian terms. The study applies modal logic, based on possible-worlds semantics and Kripke models, to clarify the conditions under which rare diseases acquire the status of social facts. By modelling behavioural change, coercion, generality and existence independent of individual manifestations, it shows how rare diseases transcend isolated clinical cases and impose structured constraints on social roles, families, institutions and policies. Empirical illustrations from international policy, employment studies, caregiver research and participation surveys are used to anchor the modal variables without treating the model as a statistical validation. The analysis argues that the transition from fragmented recognition to consolidated social fact depends on collective action, institutionalisation and normative recognition. The formalisation identifies intermediate configurations and a stabilised threshold state in which rare diseases become durable and socially binding within the model.