Publisher Summary Linguistics, as every other empirical science, is a complex mixture of theory and observation. The precise nature of this mixture is still not too well understood, and in this respect the difference between linguistics and, say, physics is probably at most one of degree. This lack of methodological insight has often led to futile disputes between linguists and other scientists dealing with language, such as psychologists, logicians, or communication theoreticians, as well as among linguists themselves. However, considerable progress is made in the understanding of the function of theory in linguistics, as a result of which theoretical linguistics has come into full-fledged existence. For theoretical purposes, as well as for practical purposes—such as machine translation and other types of mechanical processing of linguistic data—the problem to what degree simple phrase structure languages and the languages of still more complex structure can be approximated by finite state grammars is of greatest interest.