Lewis discusses authoritarian attitudes and personalities, particularly in terms of the monumental work published in 1950 by Theodor Adorno, The Authoritarian Personality. Considering a number of criticisms of Adorno's work, Lewis concludes that, whatever its conceptual and methodological limitations, it has contributed a great deal to our understanding of authoritarianism and is relevant to the study of modern history. Lewis sees the major weakness of this work as its failure to take into account the cognitive, social learning aspect of authoritarianism. Moreover, it now seems clear that there are many kinds of personalities (rather than just one kind) which have authoritarian traits. Lewis feels that it is likely that such traits have their source in deep-seated unconscious needs emerging out of early life experiences, but that they can just as easily result from cognitive learning of ideals and values which are a part of the cultural environment. Therefore, authoritarianism is likely to be caused by a multiplicity of variables in complex interaction.