Cognitive development can be construed in terms of conceptual or operational structures. The notion of‘operational structures’ is used to refer to Piaget’s dynamic form of structuralism and implies an autonomous, universal development through self-regulative processes. This position was criticized because the social aspects of development were underestimated. If development is construed in terms of ‘conceptual structures’, then ‘structure’ stands for coherence in the organization of meanings and development need not be autonomous nor self-regulative: the cultural environment has an important role to play. Although the second position thus seems promising, the worth of a conceptualization in terms of operational structures must be stressed because in this way the learning paradox can be avoided. This paradox states that it is impossible for a subject to formulate a hypothesis that does contain structures of the higher stage while being in the lower stage. Therefore, a relevant hypothesis about a new way of thinking cannot be tested and consequently never be ‘learned’. With the conceptualization of development in terms of ‘operational structures’ these objections can be neutralized because a new structure can, to a certain extent, be available for the subject in his or her actions.