Since the relationship between thought and speech is ever-changing, their progress does not run parallel. A prelinguistic phase in the development of thought and a preintellectual phase in the development of speech can be observed. Vygotsky cited a study by Koehler and Buehler to give an example of the preintellectual phase in the development of speech. Before two years of age, the development of thought and speech are separate. They melt and join at two years to initiate a new form.
Thought becomes verbal, and speech becomes rational.
Speech serves the intellect as thoughts are spoken. Language Development Language has many functions. He claimed that the primary function of speech is communication. Communicative and egocentric speech are both social with different functions. It is connected with children's thinking because it helps them overcome difficulties.