Students of the ontogenesis of human behavior have the corresponding images become increasingly less long been aware that in the early stages of the obvious. child's development it is impossible to distinguish The situation is similar as regards the analy­ between perceptual, intellectual, and operative acts. sis of relations and connections between external, With time, perception becomes relatively indepen­ practical and internal, intellectual activity. The dent of practical, operative actions, and thinking be­ work of P. Ya. Gal'perin has shown that mental ac­ comes independent of both. For this reason, general tion is formed on the basis of external material ac­ psychologists tend to forget the genetic link between tions, with real objects. On the basis of contempo­ perceptual, intellectual, and operative processes. rary psychological and genetic-epistemological re­ As a result, thinking is investigated without behav­ search, A. N. Leont'ev has given convincing proof ior and behavior without thinking, or skills are in­ of the genetic link between external and internal vestigated without perception and perception without activity. He emphasizes in particular the role of action.