Reflexive research can be grouped into five clusters with circular relations between two elements x ? x, namely circular relations between observers, between scientific building blocks like concepts, theories or models, between systemic levels, between rules and rule systems or as circular relations or x ? y between these four components.
By far the most important cluster is the second cluster which becomes reflexive through a re-entry operation RE into a scientific element x and which establishes its circular formation as x(x).
Many of the research problems in these five clusters in reflexivity research are still unexplored and pose grand challenges for future research.