Sense vs. Reference . Philosophers generally distinguish the sense of a designating term from its reference. We can refer to something by a description if the description uniquely designates some object by virtue of a certain class of descriptive qualities. Suppose now that we accept these descriptions as designations of Moses but subsequently discover that Moses really didn't write the books of Genesis and Exodus. While we may pick out Moses using various descriptions, it doesn't mean that all the descriptions we associate with Moses have to be correct for us to do so.
Realists hold that unobservable entities are like that between changes in scientific theories.
Though different theories of the electron have come and gone, all these theories refer to the same class of objects, i.e., electrons. The notion of approximate truth has never been clearly and generally defined, but the intuitive idea is clear enough. There are many qualities we attribute to a class of objects, and the set of qualities that we truly attribute to those objects increases over time. This notion means different things to different people, but is generally taken to refer to the increasing ability science gives us to manipulate the world, predict natural phenomena, and build more sophisticated technology. Convergent realists often argue for their position by pointing to the increasing success of science.