Postmodernism has revolutionised our concept of Knowledge, establishing it firmly as a relative concept that is created and valid only in a specific discourse. As a result of this re-examination, our notion of Reality has been changed irrevocably. Although many concepts, such as the dichotomy of fact and fiction, continue to be used in everyday life, they are now highly contentious from a theoretical point of view. Describing the relationship between theatre and the world that surrounds it (our everyday ‘reality’) becomes increasingly difficult in such a context, particularly with regard to theatrical forms that are characterised by their extensive use of material borrowed from the world outside the play. Using Gladiator Games and Vincent in Brixton as examples, this article demonstrates that neither the return to theoretically outdated concepts nor the radical relativism of postmodernism can offer satisfactory interpretations of documentary and biographical theatre. As a solution to this dilemma it suggests a functional approach that overcomes the schism between modern and postmodern concept.