a form of behavior characterized by physical or verbal attack. It may appear either appropriate and self-protective, even constructive, as in healthy self-assertiveness, or inappropriate and destructive. Aggression may be directed outward, against others, or inward, against the self, leading to self-destructive or suicidal actions. It may be driven by emotional arousal, often some form of frustration, or it may be instrumental, when it is used to secure a reward.