Piaget's theory

n. A set of ideas developed by the Swiss physiologist Jean Piaget, who suggested that the human mind develops in a set of stages, which he called the sensorimotor, preoperational, concrete, operational, and formal operational stages, whose order is invariant across culture. The awareness of the continuous existence of an object when it is outside our sensory field develops during the sensorimotor period and is called object permanence. During the preoperational stage the child is self-centered and unable to see things from nonsensory points of view although rudimentary language and number concepts are learned. In the stage of concrete operations the child begins to think objectively about both the world and himself/herself and begins to use operations such as reversibility, conservation, and categorization about specific objects and situations. In the stage of formal operations these are extended into abstract thinking, hypothetico-deductive reasoning, and mature moral reasoning.