Little is known about the concrete historical sources for the use of neopositivist operational criteria by the DSM-III. This paper suggests that distinct sources operated implicitly. The current usefulness of the operational approach is questioned. It is shown that: (a) in epistemology, neopositivism has been replaced by more adequate accounts; (b) psychologists rejected operational definitions because these were unable to define the majority of mental phenomena; (c) mental symptoms cannot be directly described as such, because they already make part of the psychiatric diagnosis to which they belong. In conclusion, diagnosing is based on the hermeneutical co-construction of mental symptoms. The failure of the neopositivist programme suggests that it is time to reconcile scientific formalization and semiotic activity.