Later, after Kepler’s proposals of elliptical orbits, Galileo’s telescopic observations, and Galileo’s consideration of the dynamical arguments, the balance shifted. Copernicanism had shed a number of its defects, while the traditional view had acquired some new ones. Since both approaches still faced residual problems—sciences rarely solve all the problems that lie within their domain, and there are always unanswered questions—it would still have been possible in principle to give greater weight to the virtues of traditional astronomy or to the defects of Copernicanism. By the mid-17th century, however, it would have been unreasonable to adopt any value judgment that saw the achievements of the tradition as so glorious, or the deficiencies of the rival as so severe, that Copernicanism should still be rejected. That type of valuation would be akin to preferring a decrepit jalopy, with a nonfunctioning engine and a rusting chassis, to a serviceable new car solely on the grounds that the old wreck had a more appealing hood ornament.
Although a few philosophers of science tried to make this line of response to Kuhn’s challenge more general and more precise, many contemporary discussions seem to embody one of two premature reactions. Some hold that the worries about revolutionary change have been adequately addressed and that the philosophy of science can return to business as usual. Others conclude that Kuhn’s arguments are definitive and that there is no hope of salvaging the progressiveness and rationality of science (some more-radical versions of this position will be considered in the next two sections).
Kuhn’s discussions of incommensurability challenge claims about the rationality of science by asking whether it is possible to show how the accepted views of method and justification would allow the resolution of scientific revolutions. The philosophical task here is to adapt one of the existing approaches to confirmation (Bayesianism or eliminativism, for example) to the complex contexts Kuhn presents or, if that cannot be done, to formulate new methodological rules, rules that can be defended as conditions of rationality that will apply to these contexts.
Equally, the points about incommensurability challenge the thesis that the sciences are progressive by denying the possibility of understanding the history of science as a process of accumulating truth. Here the philosopher of science needs to provide an account of progress in terms of convergence on the truth or to show how progress can be understood in other terms.
In the wake of Kuhn’s work, all of these options have been pursued. Beginning from within a Popperian framework, the Hungarian-born philosopher Imre Lakatos (1922–74) attempted to provide a “methodology of research programmes” that would understand progress in terms of increasing the “truth content” of scientific theories. The American philosopher Larry Laudan tried to show how it is possible to think of scientific progress in terms of “problem solving,” and he offered a methodology of science based on the assessment of problem-solving success. Unfortunately, however, it seems difficult to make sense of the notion of a solution to a problem without some invocation of the concept of truth; the most obvious account of what it is to solve a scientific problem identifies a solution with a true answer to a question.
The dominant position among those philosophers who tried to explain the notion of scientific progress, not surprisingly, was to try to rehabilitate ideas of convergence to the truth in the face of worries that neither truth nor convergence can be made sense of. This fueled a wide-ranging dispute over the viability of scientific realism, one that engaged philosophers, historians, and other students of science. This controversy will be the topic of the next section. Scientific realism
Issues about scientific realism had already emerged within the logical-empiricist discussions of scientific theories. Philosophers who held that theoretical language was strictly meaningless, taking theories to be instruments for the prediction of statements formulated in an observational vocabulary, concluded that the theoretical claims of the sciences lack truth value (i.e., are neither true nor false) and that use of the formalism of theoretical science does not commit one to the existence of unobservable entities. Instrumentalists suggested that terms such as electron should not be taken to refer to minute parts of matter; they simply function in a formal calculus that enables one to make true predictions about observables. By contrast, philosophers who emphasized the explanatory power of scientific theories argued that one cannot make sense of theoretical explanation unless one recognizes the reality of unobservable entities; one can understand the character of chemical bonds and see why elements combine in the ways they do if one takes the proposals about electrons filling shells around nuclei seriously but not if one supposes that electron, shell, and nucleus are mere façons de parler.
An initial dispute about scientific realism thus focused on the status of unobservables. In an obvious sense this was a debate about democracy with respect to scientific language: realists and instrumentalists alike believed that the concept of truth made good sense for a portion of scientific language—the observation language—though they differed as to whether this privileged status should be extended to scientific language as a whole. Early arguments for realism
During the 1960s and ’70s, a number of developments tipped the controversy in favour of the realists. First was Putnam’s diagnosis, discussed above, that the logical-empiricist account of the meanings of theoretical terms rested on conflating two distinctions. Second was the increasing acceptance, in the wake of the writings of Kuhn and Hanson, of the view that there is no neutral observation language. If all language bears theoretical presuppositions, then there seems to be no basis for supposing that language purporting to talk about unobservables must be treated differently from language about observables. Third was an influential argument by the American philosopher Grover Maxwell (1918–81), who noted that the concept of the observable varies with the range of available devices: many people are unable to observe much without interposing pieces of glass (or plastic) between their eyes and the world; more can be observed if one uses magnifying glasses, microscopes, telescopes, and other devices. Noting that there is an apparent continuum here, Maxwell asked where one should mark the decisive ontological shift: at what point should one not count as real the entities one thinks one is observing?
Perhaps most decisive was a line of reasoning that became known as “the ultimate argument for realism,” which appeared in two major versions. One version, developed by Salmon, considered in some detail the historical process through which scientists had convinced themselves of the reality of atoms. Focusing on the work of the French physicist Jean Perrin (1870–1942), Salmon noted that there were many, apparently independent, methods of determining the values of quantities pertaining to alleged unobservables, each of which supplied the same answer, and he argued that this would be an extraordinary coincidence if the unobservables did not in fact exist. The second version, elaborated by J.J.C. Smart, Putnam, and Richard Boyd, was even more influential. Here, instead of focusing on independent ways of determining a theoretical quantity, realists pointed to the existence of theories that give rise to systematic successes over a broad domain, such as the computation of the energies of reactions with extraordinary accuracy or the manufacture of organisms with precise and highly unusual traits. Unless these theories were at least approximately true, realists argued, the successes they give rise to would amount to a coincidence of cosmic proportions—a sheer miracle. The antirealism of van Fraassen, Laudan, and Fine