Paradigms are mega-systems of thought that explain certain realms of reality so as to shift mankind toward new visions. For example, mercantilism, Lockean limited government, species evolution, Pasteurian medicine, quantum physics, Keynesian economics, and welfare-state politics are paradigms that developed in their respective fields over the past several centuries. History is a continual process of shifting toward new paradigms in which the established thought of society is dramatically altered.