of action") is reiterated by J. William Fulbright, while a similar form occurs in Eric Hoffer's The True Believer. The revolution thus becomes established as an ideocracy, though its rise is likely to be checked by a 'political midlife crisis.' Epistemological ideologies Even when the challenging of existing beliefs is encouraged, as in scientific theories, the dominant paradigm or mindset can prevent certain challenges, theories, or experiments from being advanced. A special case of science that has inspired ideology is ecology, which studies the relationships among living things on Earth. Perceptual psychologist James J. Gibson believed that human perception of ecological relationships was the basis of self-awareness and cognition itself. Linguist George Lakoff has proposed a cognitive science of mathematics wherein even the most fundamental ideas of arithmetic would be seen as consequences or products of human perception—which is itself necessarily evolved within an ecology. Deep ecology and the modern ecology movement (and, to a lesser degree, Green parties) appear to have adopted ecological sciences as a positive ideology. Some notable economically based ideologies include neoliberalism, monetarism, mercantilism, mixed economy, social Darwinism, communism, laissez-faire economics, and free trade. There are also current theories of safe trade and fair trade that can be seen as ideologies. Ideology and the social sciences Psychological research A large amount of research in psychology is concerned with the causes, consequences and content of ideology. According to system justification theory, ideologies reflect (unconscious) motivational processes, as opposed to the view that political convictions always reflect independent and unbiased thinking. Jost, Ledgerwood and Hardin (2008) propose that ideologies may function as prepackaged units of interpretation that spread because of basic human motives to understand the world, avoid existential threat, and maintain valued interpersonal relationships. The authors conclude that such motives may lead disproportionately to the adoption of system-justifying worldviews. Psychologists generally agree that personality traits, individual difference variables, needs, and ideological beliefs seem to have something in common. Semiotic theory According to semiotician Bob Hodge:[Ideology] identifies a unitary object that incorporates complex sets of meanings with the social agents and processes that produced them. No other term captures this object as well as 'ideology'. Foucault's 'episteme' is too narrow and abstract, not social enough. His 'discourse', popular because it covers some of ideology's terrain with less baggage, is too confined to verbal systems. 'Worldview' is too metaphysical, 'propaganda' too loaded. Despite or because of its contradictions, 'ideology'