Source: John Stuart Mill, On Representative Government (1861), Chapter: I: To What Extent Forms of Government Are a Matter of Choice (page: 155).

Complete Sentence: To think that because those who wield power in society wield in the end that of government, therefore it is of no use to attempt to influence the constitution of the government by acting on opinion, is to forget that opinion is itself one of the greatest active social forces. One person with a belief is a social power equal to ninety-nine who have only interests.