Stage theorists like Piaget support the view that individuals' development can be traced through step-like stages. Each step represents forward progress, or an increase in abilities. Stage theories in general also tend to have two modes; change and growth between stages, and longer periods of stability in the stage. Usually, each new stage incorporates all of the activities or skills of the earlier stages and adds to them.
Piaget's model of cognitive development outlines the steps through which an individual moves from infancy to adult thinking. Unlike physical stages of growth, which are evident to the naked eye, cognitive growth must be measured by skills or activities. To define his stages, Piaget relied on his interpretations of how individuals represent the world around them and respond to it. Piaget considered ability to think rationally and use logic as markers of different stages.
Piaget's four stages are defined as:
Sensorimotor - usually from birth to age two
Preoperational - from age two or three to about age seven
Concrete Operational - from age seven to eleven; and
Formal Operational - from age twelve into adulthood
The fourth stage of Piaget's model, the formal operational stage, is characterized by logical thinking and the ability to understand and process abstract information. Someone in the formal operational stage of Piaget's model would be able to think about a hypothetical situation or think about and make plans for the future. A person in the formal operational stage can also understand abstract concepts such as freedom or justice. He can consider other points of view and see issues from multiple perspectives. The fourth stage is the ultimate and final stage in Piaget's model of cognitive development.