A folk theory of the effect of language on thought underlies decisions made in U.S. courts regarding language law. Previous work on folk theory has shown an internal structuring by which a premise entails subsequent terms, consistent within the framework of the folk theory's logic. An analysis of metapragmatic statements in U.S. case law materials reveals a crudely "Whorfian" premise from which a common folk theory of language builds. This theory, evident in judges' decisions and dissents, predicates the ability to understand U.S. political concepts on fluency in English. Because becoming a citizen requires comprehension of these political concepts, the folk theory links identity as a U.S. citizen with the ability to speak the English language. The appearance of a Whorfian premise in this folk theory also lends support to the suggestion by cognitive anthropologists that scientific theories are typically systematized adaptations of folk theories. (Author)