Cognitive development is associated with the changes in an individual's reasoning, thoughts and intelligence reflected by a modification in language referring to memory and concepts. Cognitive is the acquisition of the ability to reason and solve problems. Human naturally grow and develop in their cognitive functioning, learning to rationalize and communicate more effectively as they grow and develop. The ability to make decisions, as well as more accurate judgments, usually increases as an individual ages. An example of this is how a child's answers to a simple question may be very simple and an adult's answers are more complex, and use stronger vocabulary. The main theory of cognitive development was developed by Jean Piaget, a Swiss developmental psychologist interested in the intellectual development of children and concluded that children were not less intelligent than adults, they simply think differently. Children's thought processes change as they mature physically and interact with the world around them. Piaget believed children develop schema, or mental models, to represent the world. As children learn, they expand and modify their schema through the processes of assimilation the broadening of an existing schema to include new information and accommodation modification of a schema as new information is incorporated. Piaget broke childhood cognitive development through a series of four key stages spanning from birth through adolescence. In Piaget's view, early cognitive development involves processes based upon actions and later progresses into changes in mental operations. 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. Albert Einstein called Piaget's discovery "so simple only a genius could have thought of it.