One frequently encounters innuendoes, charges, allegations, threats, and rationales of conspiracy in studying the role of rhetoric in social movements. While "full discussion of competing ideas," holds high repute, "people meeting to plot some action," is disreputable and under some conditions illegal. This paper focuses on existing definitions of conspiracy in the fields of law, sociology, and political science. The author distinguishes between real as opposed to fictional conspiracies. The paper also tries to answer three questions: (1) What are the philosophic bases of conspiracy? (2) What sorts of persons are prone to believe that a conspiracy exists? (3) And what criteria must be present before a conspiracy is credible? (Author/LG)