OBJECTIVE: This paper notes the continuing problems that Royal Australian and New Zealand College of Psychiatry (RANZCP) candidates and other professionals have with the task of formulation. It re-establishes this as a problematic to be understood and reviews its intellectual history, its rationale, the tools of reasoning that it requires and the nature of the challenges that it can pose to individuals. Its premise is that an understanding of the theoretical basis of formulation is required prior to application of pedagogical tools in teaching and remediation. Four tasks of formulation implied in the definition provided in the RANZCP Formulation Guidelines for Candidates are identified, and their rationale and theoretical status reviewed. CONCLUSION: Task 1, classification, must address both diagnoses and problems. Task 2, using theory to infer meaning, ideally requires multiple models and theories in development of a set of hypotheses, using inductive inference (plausibility). Task 3, prioritising hypotheses, requires abduction, defined as inference to the best explanation. Task 4, integrating hypotheses, may aim for reconciling systems (syncretism), but is likely to use the more problematic eclecticism. The task of formulation is thus challenging but well prescribed by philosophers for thousands of years.