What holds together the things to which a general word applies and distinguishes them from other things? The idea behind Wittgenstein's treatment of linguistic regularity is that the answers given to this question by traditional theories like classical realism and nominalism are empty because there is no independent way of identifying either the universal or the specific similarity invoked. Such theories are failed mimics of science and there is no place for them in philosophy. However, it is not so easy to identify the positive content of his treatment. Why do the pupils who are being taught the meanings of general words by examples of their correct application make such outlandish mistakes?