The paper discusses a method of interpreting child's play which allows the researcher to determine exactly the aspect of play which, according to D.B. Elkonin, constitutes the motivational aspect of human activity. The author argues that the cultural prototype of complex role play is the fairy tale. Complex role play includes two steps: a challenge and an answer to the challenge. The motive is experienced by the child as real when he/she constructs the challenge and links it to the answer. The unit of play is not one isolated part, but a relationship of parts.