In this article, the fundamentals of caries diagnosis are reviewed from the three component perspectives, namely the strategy, the logics, and the tactics. Strategy concerns the objectives of the diagnostic process (i.e. why we diagnose caries). The logics describe how we assemble and evaluate the information collected and how this leads to an assessment of diagnostic value. Finally, tactics are about how we collect the information necessary to arrive at a correct diagnosis. We argue that the hitherto-dominant essentialistic caries paradigm should be replaced by a nominalistic caries concept. This allows us to circumvent the problem of a lack of a caries gold standard and to proceed in caries-diagnostic research to find the diagnostic methods that result in the best health outcomes for our patients. We also demonstrate the limitations of the medical model when attempting to understand caries diagnosis, and adhere to the BADER & SHUGARS caries script model. It is concluded that the current caries profile, characterized by lower prevalence and extent, and slower progression, has increased the need for an academic strengthening of the dental curriculum with respect to diagnostic reasoning and clinical decision-making processes.