The ArgumentWhen we actually perform an experiment, we do many different things simultaneously – some belonging to the realm of theory, some to the realms of methodology and technique; however, a great deal of what happens is expressible in terms of socially determined images of knowledge or in terms of concepts of reflectivity – second-order concepts – namely thoughts about thoughts.The emergence of experiment as a second-order concept in late antiquity exemplifies the historical development of second-order concepts; it is shown (...) to be rooted in the Sophists' cunning reason and is followed up in the work of Ptolemy, Copernicus and Galileo.Then, by way of epistemological explication, the three levels of representation of an experiment are shown to be analogous to Baxandall's three levels of representation of a picture.Finally it is shown that such an interpretation only makes sense in terms of two-tier thinking: realism, inside a conceptual framework which is chosen or arrived at, relativistically. (shrink)