Introduction. The article presents an empirical study into the correlation problems between the development of formal-logical and that of dialectical thinking at preschool age. This has been the first ever approach towards comparing these lines of thought development. The study aims to answer the questions raised by J. Piaget, K. Riegel, and M. Bassechez in their works on the relationship between dialectical and formal-logical thinking. Methods. To assess the development of dialectical thinking we used the following methods: Drawing an Unusual Tree, Cycles and What Happens to be both at the Same Time? Development of formal intellect was determined using the Piaget tests ‒ Scales, Probability and Cylinder. The data on the development of dialectical and formal-logical thinking were compared using correlational and regression statistical methods. The longitudinal study involved 87 children aged 5-6 years and 6-7- year-olds at a later stage, who attended Moscow kindergartens. Outcomes. According to the regression analysis, predictors of the success in the Probability task in the preparatory group were the scores of Piaget’s Probability and Cylinder tests and dialectical thinking measured by the Cycles and What Happens to be Both at the Same Time methods, which were assessed when preschoolers attended the older group (R = 0.606 (>0.5); F = 3.957, p=0.003). Of interest is the correlation between the Probability test outcomes and those of the Cycles method (r=0.203, p=0, 021). Discussion of outcomes. The results suggest that the formal operations of multiplication and the dialectical operations of transformation, reversal and mediation are part of a unified cognitive structure. Based on K. Riegel’s assumption, it may also be argued that it is possible to solve dialectical problems in preschool childhood.