Vygotsky suggests that much can be learned through the Context of language.
Without actually being consciously aware of the effort, the child increases the incidence of this vocal behavior (i.e., saying "da-da"), particularly in the presence of the dad.
4 Language in Context: Vygotsky and Piaget carried on a famous debate in the literature in regards to the development of concepts. Piaget suggested that concepts preceded Language.
Vygotsky advanced the notion that Language preceded concepts. It is in the context of spoken and written language that new concepts (and their symbols) dawn and are refined. Hence new words are constantly being learned as they are included in familiar discourse. This, of course, is part of what is called Motherese--a special way of talking to children that facilitates their language development.