Socialization is the process by which people learn the values and behaviors appropriate for their culture. It is shaped by both nature and nurture, as well as one's social environment. Several theorists have studied socialization and identity development. Sigmund Freud believed that identity is shaped by the id, ego, and superego as they balance internal drives with external demands. Jean Piaget identified four stages of cognitive development from sensorimotor to formal operations. George Herbert Mead viewed the self as developing through social experience and seeing oneself through the perspectives of others.