The article gives a detailed review and critical analysis of different concept investigation methods that were present in psychology at the end of 19th and at the beginning of 20th century. It shows that the method of definition fails to take into account the process of concept generation in children and works only with finished concepts. The search method developed by N. Ach and the psychological grounds underlying this method point out the determining role of the task itself in the concept development. N. Ach called his method "genetic", emphasizing that it makes it possible to trace how a word acquires its significative meaning. The article shows that there is a distinction of kind between the method of double stimulation and the previous methods. A word gradually acquires its meaning in child's activity. Thus the character of double stimulation constantly changes. Implementing the method of double stimulation enabled preliminary definitions of three stages of concept development in children: a word — an individual sign, a proper name; a word — a family sign, a proper name associatively connected with several certain objects; a word — a general concept.
Keywords: method of definition, search method, method of double stimulation, concept, word