Scientific realism is, at the most general level, the view that the world described by science is the real world as it is, independent of what it might be taken to be. Within philosophy of science, it is often framed as an answer to the question "how is the success of science to be explained?" The debate over the success of science in this context centers primarily on the status of unobservable entities apparently talked about by scientific theories. Generally, those who are scientific realists assert that one can make valid claims about unobservables (viz., that they have the same ontological status) as observables, as opposed to instrumentalism.
Scientific realism involves the two basic positions. First, it is a set of claims about the features of an ideal scientific theory; an ideal theory is the sort of theory science aims to produce. Second, it is the commitment that science will eventually produce theories very much like an ideal theory and that science has done pretty well thus far in some domains. It is important to note that one might be a scientific realist regarding some sciences while not being a realist regarding others. For example, one might hold realist attitudes toward physics, chemistry and biology, and not toward economics, psychology and sociology.
According to scientific realism, an ideal scientific theory has the following features:
Combining the first and the second claim entails that an ideal scientific theory says definite things about genuinely existing entities. The third claim says that we have reasons to believe that many scientific claims about these entities are true.
Scientific realism usually holds that science makes progress, i.e. scientific theories usually get successively better, or, rather, answer more and more questions. For this reason, many people, scientific realist or otherwise, hold that realism should make sense of the progress of science in terms of theories being successively more like the ideal theory that scientific realists describe.
The following claims are typical of those held by scientific realists. Due to the wide disagreements over the nature of science's success and the role of realism in its success, a scientific realist would agree with some but not all of the following positions.
Scientific realism is related to much older philosophical positions including rationalism and realism. However, it is a thesis about science developed in the twentieth century. Portraying scientific realism in terms of its ancient, medieval, and early modern cousins is at best misleading.