This paper considers the method of idealization and factualization as the main method of all advanced empirical science. The procedure is as follows. Some idealizing conditions are assumed: the vanishing of factors $(p_{i}=0)$ which never vanish in the real world. An idealization law is formulated -- a law which is exactly (non-vacuously) fulfilled only in an ideal model, not in any real system. Then the idealizing assumptions are abrogated one by one-it is a process of gradual factualization, of the transition (...) to the factual laws which are fulfilled in real systems. These laws may be directly applied and tested by experience. (shrink)