From the constructivist perspective, science cannot transcend the domain of experience. Scientific theories are seen as models that help to order and manage that domain. As the experiential field expands, models are replaced by others based on novel conceptual constructs. The paper suggests the substitution of ‘viability’ or ‘functional fit’ for the notions of Truth and objective representation of an experiencer-independent reality. This by-passes the sceptics’ incontrovertible arguments against certain real-world knowledge and proposes the Jean Piagetian conception of cognition as the function that generates ways and means for dealing with the world of experience.