4 SOCIAL SCIENTIST in which men exercise their capacity collectively.4 Political violence is not an ineluctable manifestation of human nature^ It is a specific kind of response to specific conditions of social existence. The capacity, but not need, for violence appears to be biologically inherent in man.® While the concept of aggression has received extensive elaboration in psychology, the frustration-anger-aggression hypothesis seems to engage the American theorists most.6 There is a variety of theoretical writings on the sources of aggression, some of it speculative, some of it based on empirical research. However, some psychological theories about the sources of aggressive behaviour can be disregarded at the outset. There is for instance little support for pseudo-psychological assertions that most or all revolutionaries or conspirators are deviants, fools or maladjusted.7 Psychodynamic explanations of the revolutionary personality may be useful for microanalysis of particular events but contribute relatively little to general theories of collective violence.® Aggressive Impulse Ted Robert Gurr categorizes the psychological assumptions about the generic sources of human aggression into three: (a) that aggression is solely instinctive; (b) that it is solely earned and (c) that it is an innate response activitated by frustration.' The instinct theories of aggression represented among others by Freud^s qualified attribution of the impulse to distructiveness or a death instinct, and by Lorenz's view of aggression as a survival-enhancing instinct, assume that most or all men have within them an autonomous source of aggressive impulses. Although there is no definitive support for the assumption, its advocates, including Freud and Lorenez, have often applied it to the explanation of collective as well as individual aggression.lo This assumption as we have already stated is evident in Hobbes's characterization of men in the state of nature, and perhaps implicit in Neiburg's recent concern for the people's capacity for outraged, uncontrolled, bitter and bloody violence,1! but plays no significant role in contemporary theories of civil strife. The second assumption that violence is a learned response, rationally chosen and dispassionately employed, is common to a number of recent theoretical approaches to collective conflict. Among theorists of revold-tion, Johnson repeatedly speaks of civil violence as purposive, as a form of behaviour intended to disorient the behaviour of others, thereby bringing about the demise of a hated social system.1 a Timasheff regards revolution as a residual, even an expedient resorted to when oiher ways of overcoming tensions have failed.1* Parsons attempt to fit political violence into the framework of social interaction theory, treating the resort to force as a way of acting chosen by the actors for purposes of deterrence, punishment or symbolic demonstration of capacity to act.14 Schelling represents those conflict theorists who explicitly assume rational behaviour and interdependence of adversaries^ decisions in all types of conflicts.18 / The third and the nWt important psychological assumption is that