AbstractThe‘crisis’debate in O.R. expresses concern at the divergence between textbook O.R. and what practitioners actually do. The debate is examined by comparing O.R., systems analysis and systems engineering. They are all wedded to logic in situations in which logic may not be paramount. The science in O.R. applies only to aggregate results, but the practitioner must deal with a specific situation. The tradition of systems thinking which emerged from organismic biology is described. It leads to a way out of the O.R.‘crisis’, by providing a formal structuring of a paradigm of learning rather than optimization. O.R. can aspire to match natural science, and pass the problems by; or it can close the textbook/practitioner gap by changing its concept of‘being scientific’.