The roots of the new work trace back to the 1920s and the Russian developmental psychologist Lev Vygotsky, who said the human mind was shaped by social activity and culture, beginning in childhood. The self, he hypothesised, was forged in what he called the ‘zone of proximal development’, the cognitive territory just beyond reach and impossible to tackle without some help. Children build learning partnerships with adults to master a skill in the zone, said Vygotsky, then go off on their own, speaking aloud to replace the voice of the adult, now gone from the scene. As mastery increases, this ‘self-talk’ becomes internalised and then increasingly muted until it is mostly silent – still part of the ongoing dialogue with oneself, but more intimate and no longer pronounced to the world. This voice – at first uttered aloud but finally only internal – was, from Vygotsky’s perspective, the engine of development and consciousness itself.