More recent philosophies of science have often tried to create a model of science and then compare philosophical conclusions with concrete research and discoveries. For instance, one could start with the assumption that (natural) science is essentially based on empirical facts or sense-data and that, consequently, all theoretical concepts or laws have to be reduced (by some correspondence rules) to a primitive empirical language or observation. Any model is useful insofar as, in accordance with some well established principles, it produces some valuable results. The difficulty with the empiricist or quasi-empirical approaches has been precisely the failure to produce any important discovery in spite of well argued guide lines; and what is still worse, some concrete examples or illustrations of these philosophies often showed misunderstanding of actual research in physics, biology, and other so-called empirical sciences.