Book excerpt: The main aim of this book is to address a fundamental question in linguistics, namely why languages are similar and why they are different. The study proposes that languages are fundamentally similar when they encode the same meanings in their grammatical systems and that languages are different when they encode different meanings. Even if languages encode the same meaning, they may differ with respect to the formal means used to code those meanings. This approach allows for a typology based on functional domains, subdomains and functions coded in individual languages. The outcome of the study is a unified approach to language theory, linguistic typology, and descriptive linguistics. The argumentation for the hypotheses and the proposed approach is supported by analyses of data from more than a dozen languages, including English, Polish, French, Wandala, Mina, Hdi, and several other Chadic languages. The study is accessible to a wide variety of linguists.