“Σώζειν τά φαινόμενα”.Realistic and antirealistic attitudes in natural science

Throughout history scientists and philosophers have discussed whether the theoretical descriptions of unobservable entities and facts were credible or not. The problem, I claim, is not due to an epistemic boundary demarcating the observable from the unobservable, but to methodological problems concerning theories, both local (as incompatibility with background theories, or lack of independent evidence) and global (as empirical underdetermination and basic human fallibility). This is seen by reviewing Celsus’ account of controversies in Hellenistic medicine, selected contemporary sources on ancient, medieval and modern cosmology, some outlines of developments in atomistic theory, wave theories, classical and relativistic mechanics, and the most recent debates on scientific revolutions.