This landmark dissertation (1961) provides a systematic introduction to systems of modal logic and stands as the first presentation of what have become central ideas in philosophy of language and metaphysics, from the 'new theory of reference' and non-linguistic necessity and essentialism to 'Kripke semantics'.

Dagfinn Føllesdal

Chapter 1 Referential and Extensional Opacity; Chapter 2 The Logical Modalities; Chapter 3 Identity of Individuals; Chapter 4 Distinctness of Individuals; Chapter 5 Singular Terms and Singular Inference; Chapter 6 Examination of the Difficulties; Chapter 7 Other Types of Opaque Contexts;