To perceive is to construct intellectually, and if the child draws things as he conceives them, it is certainly because he cannot perceive them witho… - Jean Piaget

But these structures, forming different levels, are to be regarded as succeeding one another according to a law of development, such that each one brings about a more inclusive and stable equilibrium for the processes that emerge from the preceding level.

Every observer has noted that the younger the child, the less sense he has of his own ego. From the intellectual point of view, he does not distinguish between external and internal, subjective and objective. From the point of view of action, he yields to every suggestion, and if he does oppose to other people's wills — a certain negativism which has been called "the spirit of contradiction" — this only points to his real defenselessness against his surroundings. A strong personality can maintain itself without the help of this particular weapon. The adult and the older child have complete power over him. They impose their opinions and their wishes, and the child accepts them without knowing that he does so. Only — and this is the other side of the picture — as the child does not dissociate his ego from the environment, whether physical or social, he mixes into all his thoughts and all his actions, ideas and practices that are due to the intervention of his ego and which, just because he fails to recognize them as subjective, exercise a check upon his complete socialization. From the intellectual point of view, he mingles his own fantasies with accepted opinions, whence arise pseudo lies (or sincere lies), syncretism, and all the features of child thought. From the point of view of action, he interprets in his own fashion the examples he has adopted, whence the egocentric form of play we were examining above. The only way of avoiding these individual refractions would lie in true cooperation, such that both child and senior would each make allowance for his own individuality and for the realities that were held in common.

A response is thus a particular case of interaction between the external world and the subject, but unlike physiological interactions, which are of a material nature and involve an internal change in the bodies which are present, the responses studied by psychology are of a functional nature and are achieved at greater and greater distances in space (perception, etc.) and in time (memory, etc.) besides following more and more complex paths (reversals, detours, etc.).