One of the criticisms of the operational/diagnostic criteria, generalised since DSM-III, has been that they were shaped solely to achieve the best inter-peer reliability with no considerations for validity. This does not fully reflect reality since throughout the development of the criteria, there was an effort to define and fulfil some validity requirements. However, despite several attempts to create alternative diagnostic systems, there is still a widespread misunderstanding of the epistemological foundations that support this paradigm. In this article, we intend to analyse the epistemological context in which the operational criteria (OC) emerged and some of the validation processes they have undergone since their conception. On the epistemological basis of these operational criteria (OC) the influence of Hempel has been widely discussed. However, the group from St. Louis and, also the DSM-III editors, never openly acknowledged his role and his contribution and revealed other influences such as other medical specialties (that used and validated several OC in the diagnosis of their diseases). On the other hand, contrary to what has often been mentioned there has been a continuous attempt to validate the OC since their conception. In the implementation and development of the operational paradigm, a more instrumental trend was followed, focused on utility, but with successive attempts to achieve realistic validity by searching for biological or psychological causality. The methodologies were initially expert-driven and gradually more data-driven and included some variables external to the construct itself, such as familial aggregation, diagnostic consistency over time, prognostic and other psychometric measures.