How and why societies change is of central concern to political sociology. It has been the subject of much theorising by those who wish to understand and explain the process of societal change and not a little action by those who have sought, and in some cases succeeded, in changing particular societies. Analytically it can be argued that societal change is the product of either revolution or evolution, revolution being defined, for the moment, as profound societal change precipitated by violence, and evolution as gradual societal change prompted largely though not exclusively by technological change. Such definitions, however, do no more than suggest contrasting forms of societal change and offer little by way of explanation. Moreover, it can be further argued that they are not necessarily alternative forms of change, but in certain circumstances, may be complementary. For example, revolution may lead to evolution by creating the circumstances for longer-term, evolutionary change; or evolutionary change may ultimately encounter social and political obstacles that can only be surmounted by revolutionary change. The Marxist view of revolution involves evolutionary change in the means of production creating the circumstances which render revolution inevitable.