The hypothesis, that the importance of language to mankind lies not so much in the fact that it is the means by which we cooperate and communicate with each other as in the fact that it enables each of us, as individuals and in cooperation, to represent the world to ourselves as we encounter it, is presented. In infancy, the representation is made in talk. The point is made that as we grow older we continue to talk as a means of representing the world; we also write and think. Piaget and Bruner have shown that children represent the world to themselves first in terms of perception-cum-movement. At about two years of age, the linguistic mode comes into operation. This document is concerned both with what the use of language may import into a situation and the way it does so. It is divided into eight chapters. Chapter 1 discusses the role played by speech in the formation of the child's mental processes; in Chapter 2, the methods of studying this role are examined. Chapters 3 through 7 discuss the case of speech-retarded twins. Chapter 8 concludes that with the creation of an objective necessity for speech communication, the children (i.e., the twins) were satisfactorily prepared for the acquisition of a language system; not only did they develop new forms of communication with the aid of developing verbal speech, but also there were called forth significant changes in the structure of their conscious activity. (CK)