There is not a constant correlation between thought and language. There is a relationship between thought and language, which is always changing. Vygotsky states Written speech and inner speech are monologic speech forms. Oral speech is dialogic. Vygotsky stated that inner speech was for the individual, not shared, and external speech was for communicating with others.
Internal speech is hard to express as external speech.
Vygotsky believed that egocentric speech graduates the child from social activity to more individualized activity. Social environment is the stepping-stone to higher learning. Speech is the intellect. Speech is communication. Both forms of speech, egocentric and communicative are social while serving different purposes.