Abstract This paper investigates the principles of modal development across modal domains, and the capacity of modal maps to account for these developments. The starting point is a relative newcomer in Slavic, the modal ‘have to’ + infinitive construction, which came to partially replace the older dative plus infinitive and ‘so as to’ constructions during the Middle Ages and developed across the full modal spectrum in its kernel area of West Slavic. What were the sources and the principles of this development? The paper answers these questions and draws some general conclusions about modal domains and the role of language hierarchies. The first section gives a contemporary survey, the second discusses the historical development, and the third section discusses theoretical implications.