Terminological system of L. S. Vygotsky's concept is logically-semantically analyzed. As a result general structure and thesaurus of concept is found out as well as a number of conceptual controversies. The means to deal with the latter are offered. It is argued that the higher psychic functions development was described by L. S. Vygotsky by the complex of four laws. L. S. Vygotsky's concept is a complex one and needs further investigation.