Ernest Gellner argues that cultures are crucially important in human life as constraining systems of meaning. Cultural transition means that the required characteristics are transmitted from generation to generation, leading, he shows, to both greater diversity and to far more rapid change than is possible among species where transmission is primarily by genetic means. But the relative importance of semantic and physical compulsion needs to be explored rather than pre-judged. The weakness of idealism, which at present operates under the name of hermeneutics, is that it underplays the importance of coercion, and that it presents cultures as self-justifying and morally sovereign: this line of argument, the author demonstrates, is fundamentally flawed.