Piaget suggests that concepts must precede language, but Vygotsky says that language can precede concepts.
Hence, I believe that on some occasions, the child may be exhibiting egocentric speech for practice purposes as I described.
At other times it is a phenomenon generated by the syncretistic thought processes, as Piaget conceives of it.
And still at other times, egocentric speech may be the ãtip of the icebergä providing us with a fleeting glimpse of speech being internalized to become verbal thought as Vygotsky suggests.
Speaking of the thought processes, there is another major difference between Piaget and Vygotsky. Piaget stresses that concepts must be developed first, before speech can be mapped on to it to attain meaning.
Vygotsky suggested that speech can be used to create concepts.