George Valliant classified defence mechanisms into four categories based on their level of maturity: 1) Narcissistic defences include denial, distortion, and projection which are the most primitive. 2) Immature defences used in adolescents include acting out, blocking, hypochondriasis, and regression. 3) Neurotic defences used in adults under stress include intellectualization, isolation, rationalization, and repression. 4) Mature defences seen in healthy adults are anticipation, humour, suppression, and sublimation.