According to communication theorist Harold Innis, monopolies of knowledge are created in the atmosphere of hostility between time-biased and space-biased media, wherein one tradition marginalizes the other. In this context, the term "knowledge" refers to all information and data in addition to the products of literacy and science. Paul Levinson suggests that " iteracy probably constitutes the most significant monopoly of knowledge in human history." In times when only a select number of people could read or write, the knowledge conveyed in written texts remained among the literate. It was these literate people who could decide the nature of the information that they passed on to the rest of the community. Those who control knowledge through the dominant media of a given society also control reality, in that they are in a position to define what knowledge is legitimate. Thus, monopolies of knowledge encourage centralization of power. In modern societies, language is still used to create monopolies of knowledge. Levinson uses the example of medical or legal jargon. Only those who work in these professions are aware of what is being communicated.