The aim of this paper is to discuss an inherent difficulty of PET (and fMRI) research in language production. On the one hand, language production presupposes some degree of freedom for the subject, on the other hand, interpretability of results presupposes restrictions of this freedom. This difficulty is reflected in the existing PET literature in some neglect of the general principle to design experiments in such a way that the results do not allow for alternative interpretations. It is argued that by narrowing down the scope of experiments a gain in interpretability can be achieved.