In Western psychology in this century, intense attention has been paid to the means of assisting performance: modeling, contingency managing, feeding back, instructing, questioning, and cognitive structuring. The studies of these various means of assistance have “belonged” to different theories, to different disciplines, and even to different nations. By considering them together, we can link large areas of knowledge into an articulated structure – a theory of teaching – and by linking the achievements of Western psychology to the neo-Vygotskian theory of development, the explanatory power of each is increased substantially.

In discussing the social origins of cognition, Vygotsky insisted on the primacy of linguistic means in the development of higher mental processes. The signs and symbols of speech are primary “tools” of humankind. Only when linguistic tools are integrated with the tools of physical action can the potential for full human cognitive development be reached. Indeed, he wrote that semiotics – the study of signs – is the only adequate method for investigating human consciousness. Writers in this tradition have continued to presume the primacy of interpersonal speech for the development of intrapsychological functioning, and language is featured almost exclusively in their detailed accounts of the internalization process.

This emphasis is in part due to the easily observable role of speech in the processes of internalization. Language appears to be like Mercury, the messenger who carries content from the interpsychological plane to the intrapsychological plane, a messenger with unique gifts for translation from one plane to another.