This aspect of preoperational thought is called Irreversibility. The irreversibility is the inability of the child to understand the notion of volume, does not understand that regardless of the shape of the container the amount may be the same. This type of thinking is common between 2 and 7 years, in the stage described by Piaget as Preoperational. Among the characteristics of this stage are the egocentrism and the irrationality of thought.
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