Lev Semyonovich Vygotsky (Лев Семёнович Вы́готский or Выго́тский, born Лев Симхович Выгодский [Lev Simkhovich Vygodskiy], November 17 [ November 5] 1896 – June 11, 1934) was a Soviet psychologist, the founder of a theory of human cultural and bio-social development commonly referred to as , and leader of the (also referred to as ‘Vygotsky-Luria Circle’).:
Vygotsky’s main work was in developmental psychology, and he proposed a theory of the development of higher cognitive functions in children that saw reasoning as emerging through practical activity in a social environment. During the earlier period of his career he argued that the development of reasoning was mediated by signs and symbols, and therefore contingent on cultural practices and language as well as on universal cognitive processes. He identified play, especially for young children, as the leading source of development in terms of emotional, social, physical, language or cognitive development.