*Aggression is any form of behaviour that is intented to injure someone physically or psychologically Berkowitz 1993).Aggressive behaviour is investigated by psychoanalytic theories of Freud and Lorenz based on the role of aggressive behaviour developed by innate instinct. Aggression was seen as a reaction to frustration experiences when humans seek pleasure( life instinct) . Freud suggested a second instinct the death instinct Thanatos, a tendency towards death. Freud assumed that aggressive behaviour diverts destructive energy and also reduces tension. Thus inferring the idea of Catharsis, that hostile aggression tendencies can be released in non-destructive ways such as biting homour or fantasy that will weaken the aggressive behaviour. Ethological approach by Lorenz 1963, like psychoanalytic theory notes the existence of instinctive aggressive energy, however, aggression is an innate behavioural disposition and not a drive like Freud noted, which derives from natural selection in order that aggression will increases the chances of survival. *Dollard et al 1939 in their book the Frustration and Aggression rejected the idea of death instinct and support that a person is motivated to act aggressively by previous frustration. Thus frustration is producing aggression and aggression is always a consequence of frustration. Berkowitz (1974) with his cue arousal theory, adds between frustration and aggression a basic stimulus for evoking aggression, an appropriate environmental condition (or cues). According to him through life experiences some objects become associated with aggression which foster a high value as aggressive cues i.e weapons.
*Social learning theory represent the opposite side of the debate. They assert that aggressive behaviour is learned through instrumental conditioning and / or modeling. Individuals behave in order to reach desired goals. The reainess to use this behaviour arises when it is seen as a useful means to an end in order to stop a situation which is psychologically or physically stressing due to others person control. It has been proved that people obtain different forms of aggressive behaviour through the process of instrumental conditioning (Geen and Stonner 1971- Paterson, Litman 1967). Bandura 1973 demonstrated that the initial steps for acquiring a new form of aggressive behaviour is modeling. In his experioment with Bobo doll (Bandura, Ross and Ross 1963) showed how a model could foster aggressive behaviour. A series of correlation studies shows that there is a positive association between viewing violent tv and behaving aggressive ( McCarthy et al 1975) also Leyens and Herman 1979 for a review).
*Aggressive behaviour is regulated by socially accepted and situational associated norms. The causes of aggression should not be investigated on the conditions that energise individuals drives or reduce the rational control of behaviour but on the conditions of the aggressor in which he sees his acts appropriate and justified in that situation. The instinct theories by Freud and Lorenz explain the aggressive behaviour as generating from aggressive instincts. The social learning on the other end argues that aggression is socially learnrd throught instrumental conditioning or modeling. The frustration-aggression theories explains that aggressive behaviour is motivated by a need to release aggressive energy. Other fators to consider will be the Biological theories and individual differences i.e Lagerspetz 1981 Genes, hormones, gender.