The book presents a new perspective on the essence of human language. This crucial achievement of our species is described as a communication technology collectively invented by humans to fulfill a specific communication function: the instruction of imagination. If all other communication systems in the biological world target the senses of the interlocutors, human language (vocally articulated) allows speakers to systematically instruct their interlocutors in the process of imagining the intended meaning, instead of experiencing it directly. This revolutionary function has changed human life forever, and this paper presents it as a unifying concept around which a new general theory of language appears. A very well-known evolutionary linguist, Daniel Dor identifies a set of fundamental problems in linguistics – the nature of words, the complexity of syntax, the interface between semantics and pragmatics, the causal relationship between language and thinking, language processing, the dialectic of universality and variability, language complexity, language knowledge and its acquisition, the fragility of linguistic communication and the origins and evolution of language – and shows, in all this, how its theory offers new answers to old problems, improves the significance of empirical and theoretical results in the field and identifies new directions for empirical research. In this way, the theory opens a new path towards the unification of language sciences, on both sides of the cognitive-social division.