Cognitive development refers to the acquisition of the ability to reason and solve problems. The main theory of cognitive development was developed by Jean Piaget, a Swiss developmental psychologist. Piaget broke childhood cognitive development into four stages spanning from birth through adolescence. A child who successfully passes through the stages progresses from simple sensorimotor responses to the ability to classify and create series of objects and eventually to engage in hypothetical and deductive reasoning, according to “The New Dictionary of Scientific Biography.”