“Tautology: The use of words to repeat (unnecessarily) the same statement or meaning. For example, the statement that ‘Britain is an island and surrounded by water’ is a tautology, since islands are by definition so described. Tautological explanations are similarly true by definition, or circular, and therefore unfalsifiable. Sociological explanations which located the origins of social institutions in their effects tend to take this form. Thus, for example, some early functionalist anthropologists (including Bronislaw Malinowski) were prone to argue that, because certain (exotic) social practices (such as witchcraft) existed, then they must have a social function—and one that could assume they had that function precisely because the practices themselves existed.”
Excerpted from: Marshall, Gordon, ed. Oxford Dictionary of Sociology. New York: Oxford University Press, 1994.