Repression refers to an unconscious mechanism used by the ego in keeping threatening or disturbing thoughts or reflections from becoming conscious or cognizant. Thoughts which are always repressed are those which would lead to feeling of guilt as a result of superego. For instance, within the Oedipus complex destructive or aggressive thoughts concerning similar sex parents normally are repressed. This is not always a successful defense for long term because it entails forcing disturbing ideas, memories or wishes into the unconscious, in which, although hidden, can create anxiety.
Displacement refers to redirection or rechanneling of an impulse (normally aggression) into a powerless alternative target. The target may be an object or a person which may serve like a symbolic alternative or substitute. Someone feeling uncomfortable with his/her sexual desire/need for a real individual can substitute or alternate a fetish. Someone feeling frustrated by his/her superior can for home and beat up one of the family members, get involve in cross-burnings, or kick a dog.
This is like displacement, although occurs when people are able to displace emotions into useful or constructive activity instead of destructive action. This may for instance be artistic. Most great musicians or artists have experienced unhappy lives and employed the medium or means of music to communicate. Sport is another good example of putting emotion, for instance aggression, into a constructive activity.
For instance, fixation during the oral level or stage of growth and development can later result in seeking oral pleasure or satisfaction as an adult via sucking of thumb, cigarette, or pen. Moreover, fixation at the anal stage can cause an individual to sublimate his/her desire to touch/handle with pleasure of pottery.