Reaction-Mediated Belief: A Framework of Default Ownership Attribution

When a person forms a verdict from an external source — a reaction, a remark, a dismissal — the verdict often feels like their own. This paper proposes Reaction-Mediated Belief (RMB), a framework that explains the phenomenon as a default attributionprocess. Ownership of a commitment is not encoded as a fixed feature of the commitment itself. It is attributed (or re-attributed)according to the most accessible agent representation at the time of attribution. When the external source is not attended,ownership defaults to the self in non-social contexts and to the group in social contexts. Borrowed Certainty (Yadav, 2026a) andMisattributed Sharedness (Yadav, 2026b) are the two default outcomes of this single process.The framework is specified in full. It includes a mechanism (default ownership attribution), a unit (the commitment), dynamics(parameters, thresholds, and attractors that move the system between states), an output map (agent activation × claim type→output), a four-part measure (commitment formation, source attention, agent accessibility, ownership attribution), a necessityargument (why default attribution is the only mechanism that produces both outputs), a unification argument (why BC and MSare one process), and a thresholded falsifier set. The primary empirical vulnerability — the assumption that third-party reactionsare default-read as diagnostic of the claim rather than the reactor — is stated explicitly and treated as the first test of the account.