its properties through its transformations, with the aim being to get at the object. Cognition is not based only on the object, but also on the exchange or interactions between subject and object resulting from the action and reaction of the two. Actions are coordinated in accordance with operational structures which in the first place are constituted precisely as a function of the manipulation of objects. The instrumentality of operational structures make possible the processes of relating, corresponding, ordinal estimation, measurement, classification, and prepositional structionalism. In a liquid conservation problem, (Inhelder & Sinclair, 1974, p.129) Inheler proposed that because the child became able to regard the results of pouring as the final state of a continuous process of change, he can integrate all aspects of the situation and make fewer references to the dimensions as such because he has understood the nature of their coordination. Greenfield's results with this procedure using subjects from eleven to thirteen years of age, indicated operatory solutions different form tests with eight year old. Considered in the context of the subject's reactions to various conservation problems, if they are used to back up a non-conservation answer, it shows a stage of reasoning based on the possibility of an empirical return to the initial state, and that he is not compensating for reciprocal variations of the dimensions. On the other hand, if the subject uses the same arguments to back up a conservation answer, he has understood the concepts of compensation and true reversibility. The third substage of the concrete operations period is called the concrete oper...
