The book suggests a new perspective on the essence of human language. This enormous achievement of our species is best characterized as a communication technology - not unlike the social media on the Net today - that was collectively invented by ancient humans for a very particular communicative function: the instruction of imagination. All other systems of communication in the biological world target the interlocutors' senses; language allows speakers to systematically instruct their interlocutors in the process of imagining the intended meaning - instead of directly experiencing it. This revolutionary function has changed human life forever, and in the book it operates as a unifying concept around which a new general theory of language gradually emerges. Dor identifies a set of fundamental problems in the linguistic sciences - the nature of words, the complexities of syntax, the interface between semantics and pragmatics, the causal relationship between language and thought, language processing, the dialectics of universality and variability, the intricacies of language and power, knowledge of language and its acquisition, the fragility of linguistic communication and the origins and evolution of language - and shows with respect to all of them how the theory provides fresh answers to the problems, resolves persistent difficulties in existing accounts, enhances the significance of empirical and theoretical achievements in the field, and identifies new directions for empirical research. The theory thus opens a new way towards the unification of the linguistic sciences, on both sides of the cognitive-social divide.