Piaget's epistemic subject which is also named as cognitive development theory as well, has its contribution and critics just like everything in this world has its pros and cons. The subject mentioned is probably an ideal knower or even child. Basically, this theory taught us how to knows the thought of a child and what process do children use as they construct their knowledge of the world. Piaget believed that these process are especially important in these regard such as scheme, assimilation and accommodation, organization, and equilibration. Thus, the result of these processes, according to Piaget, is that individuals go through four stages of development. A different way of understanding the world makes one stage more advanced than another. Cognitive is qualitatively different from one stage to another and so children reason in a different way from stage to another stage. Piagetian stages mean that each of Piaget's stage is age-related and consist of distinct way of thinking. There are four stages that consist of: sensorimotor, pre-operational, concrete operational, and formal operational.
First of all, Piaget's contribution is a giant in the field of developmental psychology. We cannot deny that he create a present field of children's cognitive development, a long list of masterful concepts including assimilation and accommodation, object permanence, egocentrism, conservation, and hypothetical-deductive reasoning. Besides, he also present us that the current vision of children as active and constructive thinker current belief that concepts do not emerge all off a sudden, full blown, but instead emerge through a series of partial accomplishment that lead to increasingly comprehensive understanding. Piaget also was a genius when it came to observing children. His careful observation showed us inventive ways to discover how children act on and adapt to their world. Piaget showed us some important things to look for in cognitive development, such as the shift from sensory motor stage, preoperational stage, concrete operational stage and formal operational stage thinking. He also showed us how children need to make their experience fit their schemas (cognitive framework) yet simultaneously adapt their schemas to experience. Piaget also revealed how cognitive growth is likely to occur if the context is structured to allow gradual movement to the next higher level.