The chapter discusses the concept of identity and the challenges in determining when two entities are considered the same. It explores various examples, such as events, intensional entities, and modal logics, to illustrate the complexities arising from the lack of clear criteria for identity. The author argues that the notion of identity is tied to the chosen semantical method, which determines the equivalence relations and thus the ontology of a language. The chapter critiques Frege's solution to the problem of identity, which involves the concept of "sense," and compares it with Carnap's "method of extension and intension," which emphasizes the distinction between extensions and intensions. The author concludes that the adoption of a particular semantical method, including specific equivalence relations, is equivalent to adopting an ontology. The chapter also discusses Quine's reaction to these issues, highlighting the importance of the semantical method in defining what entities exist.The chapter discusses the concept of identity and the challenges in determining when two entities are considered the same. It explores various examples, such as events, intensional entities, and modal logics, to illustrate the complexities arising from the lack of clear criteria for identity. The author argues that the notion of identity is tied to the chosen semantical method, which determines the equivalence relations and thus the ontology of a language. The chapter critiques Frege's solution to the problem of identity, which involves the concept of "sense," and compares it with Carnap's "method of extension and intension," which emphasizes the distinction between extensions and intensions. The author concludes that the adoption of a particular semantical method, including specific equivalence relations, is equivalent to adopting an ontology. The chapter also discusses Quine's reaction to these issues, highlighting the importance of the semantical method in defining what entities exist.