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Realism is a blend of metaphysics and epistemology. Metaphysically, realism claims that there is an observer-independent world; epistemologically, it claims that we can gain knowledge of that very world. In relation to science, realism asserts that, independently of our representations, the entities described by our scientific theories exist and that the theories themselves are objectively true (at least approximately). Opposed to scientific realism (hereafter just "realism") are a variety of antirealisms; notably positivism, empiricism, instrumentalism, and constructivism.
Twentieth-century positivism regarded realism as a pseudo-question external to science. Difficulties over the very possibility of a realist interpretation for the quantum theory of 1925-26 seemed to support this view (Fine 1996). The situation changed in the 1960s with the emergence of what came to be known as the "miracles" argument, namely, that unless the theoretical entities employed by scientific theories actually existed and the theories themselves were at least approximately true of the world at large, the evident success of science (in terms of its applications and predictions) would surely be a miracle (Putnam 1975; Smart 1963). During the next two decades versions of this argument became so fashionable that realism was often identified with science itself.
Despite the fashion, the argument is inconclusive because, at best, scientific success can show only that something is right about science. That could mean that science is actually getting at the truth, as the miracles argument urges, or it could just mean that science is developing reliable tools for organizing experience, perhaps using flawed representations of reality. Similar difficulties beset an influential "explanationist" variant of the argument (Boyd 1992). This version asks us to explain the evident success of science and argues that realism, with its emphasis on the truth of our theories, offers the best explanation. Among other problems, this version suffers from the defect that the conclusion in support of realism depends on the principle ("inference to the best explanation") to accept as true that which explains best (Lipton 1991). Antirealisms like instrumentalism and empiricism would deny the inference. (After all, the best may well be the best of a bad lot.) Thus the explanationist version of the "miracles" argument uses a principle of inference that begs a central question at issue between realism and antirealism -- whether truth, or some other merit, attaches to a good theory (Fine 1996; Laudan 1981).
In addition to these logical difficulties, realism has a problem with the history of science, which shows our best theories repeatedly overthrown. Inductively, this may support pessimism about the stability of current science (Psillos 1996). It also has a problem with the underdetermination of theory by evidence, which suggests that theories may have empirical equivalents between which no evidence can decide (Earman 1993; Laudan and Leplin 1991). Both considerations tend to undermine claims for the reality of the objects of scientific investigation and the truth of scientific theories.
In response, some philosophers have suggested that realism confine itself to a doctrine about the independent existence of theoretical entities (" entity realism") without commitment to the truth of the theories employing them. There are several proposals of this sort concerning which entities to advance as real. We might promote only those entities that are used experimentally to generate new knowledge or, more generally, only those we regard as causal agents (Cartwright 1983; Hacking 1983). We might take only those that prove fruitful enough to survive scientific revolutions (McMullin 1987), or only those essential in specific cases of explanatory or predictive success (Kitcher 1993) or only those entities that stand out as supported by especially excellent scientific evidence (Newton-Smith 1989). Finally, we might just plead that surely some entities must be real, without specifying which ones (Devitt 1984). Unfortunately for entity realism, it is not clear that such criteria overcome the strategies that challenge realism in general. In particular these proposals do not seem to discriminate effectively between real entities and reliable (or useful) constructs -- and so between realism and instrumentalism (Fine 1986).
A number of fresh alternatives to realism have developed recently. Principal among them are Putnam's "i nternal realism" (1981, 1990), van Fraassen's "constructive empiricism" (1980), and what Fine calls the "natural ontological attitude," or NOA (1996). Internal realism is a perspectival position allowing that scientific claims are true from certain perspectives but denying that science tells the whole story, or even that there is a whole story to tell. There could be other versions of the truth -- different stories about the world -- each of which it may be proper to believe. Van Fraassen's constructive empiricism eschews belief in favor of what he calls commitment. In contrast with realism, constructive empiricism takes empirical adequacy (not truth) as the goal of science, and when it accepts a theory it accepts it only as empirically adequate. This involves commitment to working within the framework of the theory but not to believing in its literal truth. Fine's NOA is a minimal attitude that urges critical attention to local practice without imposing general interpretive agendas on science, such as goals for science as a whole or blanket empiricist limitations on knowledge. NOA regards truth as basic but, seeing science as open, it challenges general prescriptions for scientific truth, including the perspectivalism built into internal realism and the external-world correspondence built into realism itself. Despite their differences, these alternatives share with realism a basically positive attitude toward science. A contrary suspicion attaches to constructivism (Barnes, Bloor, and Henry 1996; Galison and Stump 1996; Latour 1987; Pickering 1984; Searle 1995).
Constructivism opposes realism's claim that in order to understand science we must take scientists to be exploring a world not of their own making. Inspired by developments in the history and sociology of science, it maintains instead that scientific knowledge is socially constituted and that "facts" are made by us. Constructivism emphasizes agency and (like NOA) sees unforced judgments throughout scientific activity. In their studies constructivists bracket the truth-claims of the activity under investigation and try to address scientific practice using little more than common sense psychology and an everyday pragmatism with respect to the familiar objects of experience. To the extent to which these studies succeed in understanding science they paint a picture quite different from realism's, a dynamic and open picture that challenges not only the arguments but also the intuitions on which scientific realism rests.
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