Otto Jespersen sets out to establish a biological and biographical science of language, arguing that a language has no separate existence apart from the human beings who speak and remember it. The study begins with an historical survey of linguistic science before the nineteenth century, examining how antiquity, the Middle Ages, and eighteenth-century thinkers such as Herder and Rousseau approached the origin of speech. The work then explores the great turning-point of the nineteenth century, detailing the breakthroughs of Sanskrit scholarship, Friedrich von Schlegel, Rasmus Rask, Jacob Grimm, and Franz Bopp, which together laid the foundations of comparative grammar. The middle chapters investigate the nature of language acquisition in children, showing how sounds, words, and grammar are mastered through a combination of physiological exercises, imitation, and analogy.
Jespersen then examines the individual in relation to the world, analyzing the influence of foreigners, pidgin languages, and the social causes of linguistic change. Finally, the study addresses the core questions of linguistic development, etymology, sound symbolism, and the ultimate origin of human speech. While the author demonstrates how languages constantly shift and grow, he provides a comprehensive system for understanding linguistic evolution as a continuous human activity rather than a static system.