Jean Piaget was a Swiss psychologist who developed a theory of cognitive development with four distinct stages. The sensorimotor stage occurs from birth to age 2 where intelligence develops through interactions with physical environment. The pre-operational stage is from ages 2 to 7, where symbolic thought and language develops but thinking remains egocentric. During the concrete operational stage from ages 7 to 11, logical and reversible thought emerges regarding concrete ideas. Finally, in the formal operational stage from ages 11 through adulthood, abstract reasoning abilities allow for logical problem solving of complex ideas. Piaget's stages describe how children's cognitive abilities progress as they interact with their environment.