Swiss biologist Jean Piaget eventually came to think that intelligence is a form of adaptation, in which each individual, through the two processes of assimilation and accommodation, constructs knowledge. He theorized that as children interact with their physical and social environments, they organize information into groups of interrelated ideas called schemes. When children encounter something new, they must either incorporate it into an existing scheme or create an entirely new scheme to deal with it.
             Piaget also believed that intellectual development occurs in four distinct stages. The sensorimotor stage begins at birth, and lasts until the child is approximately two years old. At this stage, the child cannot form mental representations of objects that are outside his immediate view, so his intelligence develops through his motor interactions with his environment. The preoperational stage typically lasts until the child is 6 or 7. According to Piaget, this is the stage where true "thought" emerges. Preoperational children are able to make mental representations of unseen objects, but they cannot use deductive reasoning. The concrete operations stage follows, and lasts until the child is 11 or 12. Concrete operational children are able to use deductive reasoning, demonstrate conservation of number, and can tell apart their viewpoint from that of other people. Formal operations is the final stage. Its most significant feature is the ability to think conceptually.
             He also introduced several ideas explaining differences in logical thinking in children and young adults. A central belief of Piaget's theory of epistemology (origins of knowledge) is that increasingly more complex intellectual processes are built on the basic foundations laid in earlier stages of development. An infant's physical explorations of his environment form the basis for the mental representations he develops during his pre
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