Vygotsky claimed that we are born with four elementary mental functions: attention, sensation, perception and memory. It is our social and cultural environment that allows us to use these elementary skills to develop and finally gain higher mental functions.

Vygotsky also established an explicit connection between speech and mental concepts, arguing that inner speech develops from external speech via a gradual process of internalization. This means that thought itself develops as a result of conversation. Therefore younger children who don't finish this process can only think out loud. Once the process is complete inner speech and spoken language become independent.

While Jean Piaget concluded that children's cognitive development happens in stages, Vygotsky rejected his ideas and believed that children develop independently of specific stages as the result of social interactions.