A theoretical framework which led to Piaget’s theory of cognitive development. Piaget described the stages of cognitive development in humans as a chronological series of stages. At each stage the cognitive development increased. The stages were named: 1. sensorimotor stage (0-2 years); intelligence development is seen in motor actions. 2. pre-operation stage (3-7 years) where intelligence is intuitive. 3. the concrete operational stage (8-11 years); intelligence is logical. 4. formal operations (12-15 years); intelligence, especially thinking, involve abstraction.