There are, broadly, three modern definitions at work in discussions about intellectuals. First, “intellectuals” as those deeply involved in ideas, books, and the life of the mind. Second, “intellectuals” as a recognizable occupational class consisting of lecturers, professors, lawyers, doctors, scientists, engineers, etc. Third, “cultural intellectuals” are those of notable expertise in culture and the arts, expertise which allows them some cultural authority, which they then use to speak in public on other matters.
'Men of letters'
The expression "man of letters", has been used in many cultures to describe contemporary intellectuals. The term implied a distinction between those "who knew their letters" and those who did not. The distinction thus had great weight when literacy was not widespread. "Men of letters" were also termed literati (from the Latin), as a group; this phrase may also refer to the 'citizens' of the Republic of Letters. Literati survives as a term of abuse and is used in journalism. Literatus, in the singular, is rarely found in English - the English term is litterateur (from the French littérateur). The Republic of Letters grew during the late 1700s in France in salons, many of which were run by women. The term is rarely used to denote "scholars".
Greek usage of the expression
In Greece the expression "Learn your letters" finds widespread use in everyday life, especially by the surviving older generations. Its meaning is equivalent to "Study hard" and "learn an intellectual trade".
Because of the agricultural background of Greece, the term "man of letters" also signifies the opposite of the usual trades of builder and farmer. In this context, these hand-driven trades are often pointed out as examples to be avoided when parents suggest to a young person to "become a man of letters" in order to live an easier life.
Nineteenth-century English usage
By the late eighteenth century, literacy was becoming more widespread in countries such as the United Kingdom. The concept of a "man of letters" shifted to a more specialised meaning, as one who made his living by writing about literature - usually not creative writers as such, but rather essayists, journalists and critics. This kind of activity was gradually replaced in the twentieth century by a more academic approach, and the term "man of letters" fell into disuse, to be replaced by the more generic term "intellectual", which first came into common use at the end of the nineteenth century, when it was used as a term for the defenders of Dreyfus, see below. The rise and fall of the term "man of letters", and indeed of the activity it described, is charted by Gross (1969); see also Pierson (2006).
Modes of 'intellectual class' in nineteenth-century Europe
Samuel Coleridge speculated early in the nineteenth century on the concept of the clerisy, a class rather than a type of individual, and a secular equivalent of the (Anglican) clergy, with a duty of upholding (national) culture. The idea of the intelligentsia, in comparison, dates from roughly the same time, and is based more concretely on the status class of 'mental' or white-collar workers. Alister McGrath in The Twilight of Atheism (2004) comments (p.53) that '[t]he emergence of a socially alienated, theologically literate, antiestablishment lay intelligentsia is one of the more significant phenomena of the social history of Germany in the 1830s', and that '... three or four theological graduates in ten might hope to find employment [in a church post]'.
From that time onwards, in Europe and elsewhere, some variant of the idea of an intellectual class has been important (not least to intellectuals, self-styled). The degrees of actual involvement in art, or politics, journalism and education, of nationalist or internationalist or ethnic sentiment, constituting the 'vocation' of an intellectual, have never become fixed. Some intellectuals have been vehemently anti-academic; at times universities and their faculties have been synonymous with intellectualism, but in other periods and some places the centre of gravity of intellectual life has been elsewhere.
One can notice a sharpening of terms, in the latter part of the nineteenth century. Just as the coinage scientist would come to mean a professional, the man of letters would more often be assumed to be a professional writer, perhaps having the breadth of a journalist or essayist, but not necessarily with the engagement of the intellectual.
The Dreyfus affair in France at the end of the nineteenth century is often indicated as the time of full emergence of the intellectual in public life; particularly as concerns the role of Émile Zola, Octave Mirbeau and Anatole France, in speaking directly on the matter. The term "intellectual" became better known from that time (and the derogatory implication sometimes attached). The use of the term as a noun in French has been attributed to Georges Clemenceau in 1898.
Societal role of intellectuals
Intellectuals have been viewed as a distinct social class.
Often significantly contributing to the formation and phrasing of ideas, intellectuals are both creators and critics of ideology. Australian writer Rhoderick Gates defined intellectuals as "priests in a secular society, whose role is to uphold Establishment truths and power" in Intellectuals, Society and Oligarchy, 1999, p.1. However some intellectuals in the Establishment could be described as dissenters against the Establishment, such as US linguist and writer Noam Chomsky.
In many definitions, intellectuals are sometimes perceived to remain impervious to propaganda, indoctrination, and self-deception. Due to the co-option of intellectuals by the Soviet Union, the Third Reich and by other regimes and ideologies, the question has been raised how and why intellectuals can be vulnerable to indoctrination in spite of their perceived intelligence. One possible answer was concluded in the Milgram experiment. The Milgram experiment was a seminal series of social psychology experiments conducted by Yale University psychologist Stanley Milgram, which measured the willingness of study participants to obey an authority figure who instructed them to perform acts that conflicted with their personal conscience. The study found that ordinary people can become agents in a terrible destructive process, even when the destructive effects of their work become patently clear. Despite intelligence or intellectual capacity, when people are asked to carry out actions incompatible with fundamental standards of morality, relatively few people have the resources needed to resist authority. Another suggested reason for this is the intellectuals' constant criticism of ideological systems in an attempt to improve them, which often leads to seeking superior alternatives in foreign models, due to the fact that foreign models are not seen in action and thus cannot be accurately gauged before implementation.
Strictly a doctrine about the possibility of deriving knowledge from reason alone, intellectualism can stand for a general approach emphasising the importance of learning and logical thinking. As a philosophical doctrine it is usually termed Rationalism. Criticism of this attitude, sometimes summed up as Left Bank, caricatures intellectualism's faith in the mind and puts it in opposition to subjective experience, religious faith, emotion, instinct, and primitivist values in general.
Academics and public intellectuals
In some contexts, especially journalistic speech, intellectual refers to academics, generally in the humanities, especially philosophy, who speak about various issues of social or political import. These are so-called public intellectuals — in effect communicators.
The term masks an assumption or several, in particular on academia, for example that intellectual work goes on generally in private, and there is a gap to society that requires bridging. In general practice, 'intellectual' as a label is more consistently applied to fields related to culture, the arts and social sciences than it is to working disciplines in the natural sciences, applied sciences, mathematics or engineering. Critics argue that intellectuals in these fields may remain as susceptible to indoctrination, self-deception, and propaganda as the general public because they suffer from the same human prejudices and weaknesses.
Outside the West
In ancient China literati referred to the government officials who formed the ruling class in China for over two thousand years. These scholar-bureaucrats were a status group of educated laymen, not ordained priests. They were not a hereditary group as their position depended on their knowledge of writing and literature. After 200 B.C. the system of selection of candidates was influenced by Confucianism and established its ethic among the literati. The Hundred Flowers Campaign in China was largely based on the government's wish for a mobilization of intellectuals; with very sour consequences later.
The security of a religious group depends on spiritual unity, not on theological uniformity. A religious group should be able to enjoy the liberty of freethinking without having to become "freethinkers".
- de Huszar, George B., ed., 1960 The Intellectuals: A Controversial Portrait. Glencoe, Illinois: The Free Press. Anthology with many contributors).
- Furedi, Frank, 2004, Where Have All The Intellectuals Gone?, Continuum,
- Michael McCaughan, True Crime: Rodolfo Walsh and the Role of the Intellectual in Latin American Politics, Latin America Bureau 2000, ISBN 1-899365-43-5
- Gross, John, 1969 The rise and fall of the man of letters. (Pelican edition, 1973).
- Jennings, Jeremy and Kemp-Welch, Anthony, eds. (1997), Intellectuals in Politics: From the Dreyfus Affair to Salman Rushdie.
- Johnson, Paul, Intellectuals. Perennial, 1990, ISBN 0-06-091657-5. A highly ideological onslaught discussing Rousseau, Shelley, Marx, Ibsen, Tolstoy, Hemingway, Bertrand Russell, Brecht, Sartre, Edmund Wilson, Victor Gollancz, Lillian Hellman, Cyril Connolly, Norman Mailer, James Baldwin, Kenneth Tynan, Noam Chomsky, and others
- Piereson, James, 2006 The rise & fall of the intellectual The New Criterion, September 2006
- Posner, Richard A., 2002, Public Intellectuals: A Study of Decline, Cambridge, MA: Harvard University Press, ISBN 0-674-00633-X.
- Kidder, David S., Oppenheim, Noah D., "The Intellectual Devotional: Revive Your Mind, Complete Your Education, and Roam Confidently with the Cultured Class", 2006. ISBN 1-59486-513-2
- The vanishing man of letters: Part One, Contemporary Review 
- The vanishing man of letters: Part Two Contemporary Review 
- A Special Supplement: The Responsibility of Intellectuals By Noam Chomsky, February 23, 1967
- Posner's table of 600+ public intellectuals classified by such variables as sex, professional and disciplinary affiliation, political leaning, media affiliation, Web hits, and scholarly citations.