Egocentric speech develops into internal speech. Vygotsky added frustrations and difficulties to Piaget's experiments. Words play a central part not only in the development of thought but in the historical growth of human consciousness as a whole. A word is a microcosm of human consciousness. Human beings are not limited to their biological inheritance, as other species are, but are born into an environment that is shaped by the activities of previous generations.
Humans have the capacity to continue to develop intelligence.
Vygotsky differentiated between our higher and lower mental functions. In contrast, our higher mental functions develop through social interaction, being socially or culturally mediated. Behavioral options are limited when functioning occurs at an elementary level. Without the learning that occurs as a result of social interaction, without self-awareness or the use of signs and symbols that allow us to think in more complex ways, we would remain slaves to the situation, responding directly to the environment. Mediation occurs through the use of tools or signs of a culture.