Scientific realism

Scientific realism is a view in the philosophy of science about the nature of scientific success, an answer to the question "what does the success of science involve?" The debate over what the success of science involves centers primarily on the status of unobservable entities (objects, processes and events) apparently talked about by scientific theories. Roughly put, scientific realism is the thesis that the unobservable things talked about by science are little different from ordinary observable things (such as tables and chairs).

Main features of scientific realism
Scientific realism involves 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 very realist attitudes toward physics, chemistry and biology, while being less realist toward economics, psychology and sociology.

According to scientific realism, an ideal scientific theory has the following features:
 * The claims the theory makes about unobservables are either true or false, and they are true or false depending on whether the entities talked about by the theory exist and are correctly described by the theory. This is the semantic commitment of scientific realism.
 * The unobservables described by the scientific theory exist objectively and mind-independently. This is the metaphysical commitment of scientific realism.
 * There are reasons to believe some significant portion of what the theory says about unobservables. This is the epistemological commitment.

Combining the first and the second claim entails that an ideal scientific theory says true things about genuinely existing unobservable entities. The third claim says that we have reasons to believe that the things said about unobservable entites are true.

Scientific realism usually holds that science makes progress, i.e. that scientific theories usually get successively better. For this reason, many people, scientific realist and 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.

History of scientific realism
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.

Scientific realism is developed largely as a reaction to Logical positivism. Logical positivism was the first philosophy of science in the twentieth century and the forerunnner of scientific realism, holding that a sharp distinction can be drawn between observational terms and theoretical terms, the latter capable of semantic analysis in observational and logical terms.

Logical positivism encountered difficulties with: These difficulties for logical positivism suggest, but do not entail, scientific realism, and lead to the development of realism as a philosophy of science.
 * the verification theory of meaning (for which see Hempel (1950))
 * troubles with the analytic-synthetic distinction (for which see Quine (1950))
 * the theory ladenness of observation (for which see Kuhn (1970) and Quine (1960))
 * diffculties moving from the observationality of terms to observationality of sentences (for which see Putnam (1962))
 * the vagueness of the observational-theoretical distinction (for which see Maxwell (1962))

The development of realism as an alternative to positivism also lead to arguments to support realism as a philosophy of science.

Realism became the dominant philosophy of science after positivism. Bas van Fraassen developed constructive empiricism as an alternative to realism. Responses to van Fraassen have sharped realist positions and lead to some revisions of scientific realism.

Arguments for and against scientific realism
One of the main arguments for scientific realism centers on the observation that scientific knowledge is progressive in nature, and that it is able to predict phenomena successfully. Many realists feel the operational success of a theory lends credence to the idea that its more unobservable aspects exist, because they were how the theory reasoned its predictions. For example, a scientific realist would point out that science must derive some ontological support for atoms from the outstanding phenomenological success of all the theories using them.

On the other hand, Pessimistic induction, one of the main arguments against realism, argues that many previously successful scientific theories achieved their predictive success through the postulation of the existence of entities which later, even more successful, theories showed did not exist. It is then argued that we should expect for our theories to be replaced by newer ones which postulate a different set of unobservables.

Also against scientific realism social constructivists point out that scientific realism is unable to account for the rapid change that occurs in scientific knowledge during periods of revolution. Constructivists may also argue that the success of theories is only a part of the construction.

The other main argument against scientific realism, deriving from the underdetermination problem, is not so historically motivated as these others.