Hyperintensionality and Synonymy Levin Hornischer Abstract: We investigate the related and important concepts of synonymy and hyperintensionality (i.e. criteria for identity that are more fine-grained than necessary equivalence). We show how, for every language, validity uniquely determines a co-hyperintensionality relation (that ensures substitution salva veritate). The ordering of operators by their ability to discriminate sentences is not linear (e.g. truthmaking and necessity are incomparable). However, co-hyperintensionality is not a cognitively adequate individuation of content. Instead, we analyze cognitive synonymy (or likeness in cognitive role) conceptually via defeasible rules, algorithmically via logic programming, and neurally by constructing an appropriate neural network. This explains the contextual stability of synonymy (given by the rules) and its flexibility (some contexts defeat the rules). We introduce the notion of a scenario that has a representational component (like Fregean senses) and an interpretational component (like a possible world). Scenarios can be grounded, e.g., in neural networks, and they have a constructive notion of distance. We use them to provide a hyperintensional semantics including a counterfactual and belief and conceivability operators. This scenario framework allows reconstructing many notions of synonymy. We provide a logic for content identity in scenario semantics. We observe that it is inconsistent to hold both (i) if no scenario distinguishes two sentences, they are identical in content, and (ii) content identity entails identity in subject matter. Scenario semantics satisfies (i) and Fine’s logic of analytic containment satisfies (ii), though it is not the most coarse-grained one above scenario semantics. A semantics with a content-granularity like analytic containment requires moving from scenarios to sets of scenarios. We conclude our investigation with a pluralistic conception of synonymy: because of the sheer number of notions of synonymy, and because it is the only way to reconcile the many opposing features of synonymy.