Summary Research is regarded as transformations of complexes composed of knowledge, problems and (hardware and software) instruments. Sequences of such transformations are embedded in human settings in which they are given directions. Problems and the work of solving them are divided into empirical and theoretical ones. In an advanced science like physics empirical and theoretical work are interrelated by means of flows of problem-generating information. Empirical and theoretical researchers work also on problems of their own making. Residuals of knowledge which (...) cannot be systematized at the same rate as it is produced as well as clashes between new and old knowledge are potential starting points of new lines of research. (shrink)