Generalized shared reality arises in brief interactions from structured social inferences about commonality

After just a few minutes of conversation, we may feel ``on the same page'', or profoundly disconnected, based on thin evidence.How do brief interactions produce such sweeping expectations about what we share with others?We propose that generalized shared reality arises through structured inductive inference: people leverage intuitive knowledge about how beliefs covary to generalize from sparse observations.Using a text-based chat paradigm, we asked pairs of strangers to discuss either shared or opposing beliefs, and compared these conversations with a control condition in which participants simply learned their partner's stance.We observed systematic generalization gradients: after observing agreement or disagreement on one topic, people expected more or less similarity on related topics, respectively. Real conversations relaxed thresholds for inferring commonality, amplifying these expectations.Participants who inferred broader commonalities reported stronger shared reality, linking these structured inferences to the subjective experience of connection.A Bayesian factor model that leverages population-level belief covariance captured participants' generalization patterns, whereas an egocentric heuristic model did not. Large language models given full conversation transcripts better matched participants' judgments about broader commonalities, confirming that conversations convey structured information beyond a single observed stance. Taken together, these findings illuminate how brief interactions can systematically shape our expectations of what we have in common with others through structured inductive inference over belief covariance.