Adjudicating the realism/anti-realism debate in science often involves discussion of ‘miracles,’ the ‘observable/unobservable distinction,’ and ‘underdetermination’. Pick one of these three areas and develop an argument for realism or anti-realism in terms of it. Don’t forget to assess the argument.

The realism/anti-realism debate in science often hinges on the nature of and relationship between observables and unobservables. Anti-realists argue that scientists can have no actual knowledge of unobservables, and therefore should treat theories about unobservables agnostically: however useful the models may be, they should not be considered to correspond to truth about reality. For example, anti-realists argue that hypotheses about the nature of fundamental particles such as quarks and electrons should not be taken as if quarks and electrons actually exist, but only as pragmatically useful, with no way even in principle of determining whether such things actually exist.

In fact, any attempt to consider the relationship between observables and unobservables ultimately points instead toward a (critical) realist account of science. Any attempt to distinguish sharply or clearly in principle between observables and unobservables fails, for two reasons: first, the claim that “unobservables” as such exist in a strict sense; and second, that, the relationship between “observable” and “unobservable” falls along a spectrum.

In the first case, anti-realists use “unobservable” to mean anything not directly observable by human senses. However, to declare such objects in principle unobservable is to beg the question, since the point under debate is precisely whether things detected indirectly—electron traces in a gas cloud, for example—are being observed or simply hypothesized. Anti-realists must first establish in an in-principle sense a sharp distinction between that which is indirectly observed and that which is directly observed. Realists, by contrast, note that indirect observation is rightly considered reliable in the realm of ordinary experience. It is reasonable to conclude that the wind is blowing from seeing its effects on trees even if sitting inside a closed room with no direct experience of the wind. Indirect observations still count as observations, and are clear signals of the real presence of a thing being observed. Whether it is observed directly or indirectly does not determine whether it is observed at all.

This also extends into the second case: a realist view rightly makes sense of the way things are more or less directly observable. On one end are those phenomena which can be detected through (normal, healthy) human senses such as hearing or vision. Moving down toward the not-directly-observable spectrum, scientists use various sorts of equipment to enhance their ability to observe: telescopes, when looking at things inaccessible to ordinary human sight because of distance; and microscopes, when examining things inaccessible to ordinary human sight because of size. In both cases, however, there is no clear line distinguishing the “observable” and the “unobservable”—only a spectrum of more- or less-directly-observable phenomena. Insects may be observed with the unaided human eye, bacteria with optical microscopes, individual molecules of materials with electron microscopes. In each case, the same principle is at work in the observation: light bouncing off an object and being received.

The anti-realist may object that this is not so: the fact that the distinction between observables and unobservables is blurry does not mean it does not exist. To borrow an example from Okasha: the line between “bald” and “hirsute” may be fuzzy (pun intended), but it is still possible to identify a bald man. Even granting the in-principle distinction between “observable” and “unobservable,” however, the objection fails to establish the strong claim made by anti-realists. It does not establish that the items in question are in fact unobservable (especially when confronted with the realist argument for indirect observation). Nor does it establish that scientists would be in principle incapable of correctly modeling unobservables. At most, it establishes that unobservables may exist.

Thus, it is reasonable to suppose that though current models of astronomical behavior, or of quantum mechanics, or gravity, or any other only-indirectly-observable phenomena may be incomplete or partial, they nonetheless represent something actual. The wind really is blowing. There really an electron leaving a trail in the gas chamber.