Eclecticism in social work has been criticised because interventions may be based on theories that have incompatible basic assumptions. The author offers a structural analysis of theories informing social work practice, according to each theory's basic assumptions about the nature of human society as either conflict or consensus, and human behaviour as a product of either free will or determinism. Four basic paradigms of practice in social work are created as quadrants within a circle and labelled, respectively, as the functionalist, existentialist, humanist and structuralist paradigms. The structure is then modified to establish a fifth ‘heuristic paradigm’ as an inner circle. The author suggests that heuristic paradigm theories are those that best accommodate the paradoxical coexistence of free will and determinism, and also conflict and consensus. Heuristic practice is therefore not seen simply as intuitive eclecticism, but an active and reflective use of various theories as ‘heuristic tools’ to shape practice interventions and thereby build practice wisdom.