IS THIS SCIENTIFIC REALISM?

The final objection, possibly the most important, is that whatever Perrin proved in his argument, even if by means of his experiments he did prove that molecules exist, this is not scientific realism.

An objection of this sort will be raised by anyone, realist or antirealist, with a more demanding view of what scientific realism requires. Various candidates for scientific realism have been suggested in recent years by proponents as well as critics; three prominent ones will be noted.

(1) Scientific realism is a view about truth and reference in scientific theories generally. For example, Richard Boyd^[129] and Stathis Psillos,^[130] defenders of scientific realism, and Larry Laudan,^[131] a severe critic, all claim that scientific realism involves a number of central theses, including these:

(A) Scientific theories (at least in the “mature” sciences) are typically approximately true, and more recent theories are closer to the truth than other theories in the same domain.

(B) The observational and theoretical terms within the theories of a mature science genuinely refer (roughly, there are substances in the world which correspond to the ontologies presumed by our best theories).

(C) Successive theories in any mature science will be such that they “preserve” the theoretical relations and the apparent referents of earlier theories (that is, earlier theories will be “limiting cases” of later theories).

(D) Acceptable new theories do and should explain why their predecessors were successful insofar as they were successful.

This is Laudan's formulation (pp. 219-20). To these theses Boyd adds:

(E) The reality which scientific theories describe is largely independent of our thoughts or theoretical commitments (p.42).

Thesis (E) relates scientific realism to a core idea of what is sometimes called metaphysical realism, namely, that there is a mind- and theory-independent way the world is; to this core idea it adds the claim that scientific theories describe such an independent world.^[132] ^{^[133] ^[134]}

Even if Perrin proved that molecules exist, he did not prove theses (A)-(E), or even make them probable.

Nothing Perrin did establishes or makes probable claims about scientific theories generally, or even about ones in mature sciences. Nor did Perrin establish that there is a mind- and theory-independent world or that theories in the mature sciences describe such a world approximately correctly.

(2) Scientific realism is a view about the aim of science. Here is van Fraassen's formulation:

Science aims to give us, in its theories, a literally true story of what the world is like; and acceptance of a scientific theory involves the belief that it is true. This is the correct statement of scientific realism.²⁸

Van Fraassen distinguishes the aim of science, as a type of activity, from the aims of particular scientists, which may include fame and fortune.²⁹ Now, proving that molecules exist does not establish that the aim of science is to provide a literally true story of the world (or to satisfy any other broad conditions, such as describing natural kinds and dependencies), not even if this were Perrin's aim in the case of molecules. One would need to show more than this to establish scientific realism in the present sense. (I shall return to this in section 7).

(3) The scientific realism of interest to philosophers is not itself an internal scientific question, to be settled by scientific reasoning, but an external one concerning the adequacy of the scientific representation of the world. It cannot be established by empirical means. Both Rudolf Carnap^[135] and Arthur Fine^[136] have defended a distinction between internal and external questions. Their views about internal questions are somewhat similar, although they take very different positions on external questions.

For Carnap, the question of whether molecules exist can be approached in two ways. First, it can be treated as an empirical question within what Carnap calls a “linguistic framework,” which contains rules of language and of inference, including rules governing what counts as evidence for what.

Considered as an internal question within a framework permitting “theoretical terms” for unobservable entities, the answer to whether molecules exist can be determined empirically by the sorts of arguments from experiments Perrin provided. But this is not what philosophers usually have in mind when they assert (or deny) scientific realism with respect to theoretical entities such as molecules. For these philosophers, the question is an external one concerning the adequacy of the “theoretical entity” framework within which molecular claims are made. For Carnap, the claim that the framework is adequate is not a claim about its relationship to a framework-independent world. It is a pragmatic claim about the employability of the framework based on features such as simplicity, ease of use, and familiarity. Accordingly, different frameworks can be adopted, some of which have no terms for unobservables such as molecules. Some frameworks may be more user-friendly than others, but none is “correct” or “incorrect.”

Carnap's internal questions are part of what Fine calls the natural ontological attitude (NOA). So, Fine can agree, Perrin established the existence of molecules by means of his experiments. In this internal sense, an antirealist can agree with a realist about what Perrin accomplished scientifically. What a realist does, according to Fine, is to step outside of scientific activity and claim that theories correspond to reality. Fine does not endorse Carnap's line that such a claim is pragmatic. Rather, he says simply that what the realist is doing when he steps outside of scientific activity is tantamount to pounding the table and saying “Molecules exist, really!” This adds only emphasis to the internal claim. Fine, then, advocates NOA, which he regards as different from both realism and antirealism but as something that realists as well as antirealists can accept.

Both Carnap and Fine could agree that Perrin proved empirically that molecules exist, where the latter claim is understood as one internal to science (as part of NOA).

For Carnap and Fine, Perrin did not prove, nor could he, that a framework containing terms for molecules corresponds to reality in some external sense. So if, as is typical, scientific realism is construed as an external doctrine, Perrin did not establish scientific realism. For Fine, neither Perrin nor anyone else could establish realism in an external sense. For Carnap, Perrin showed, by using the framework he did, at best that it was useful; he did not show that it is the only or the most useful one for dealing with questions involving Brownian motion.

These three views about scientific realism represent a spectrum of positions. Perrin's arguments do not establish scientific realism in a sense of that term advocated by any of the philosophers noted. So is Salmon mistaken in his claim that Perrin provided a valid experimental argument for scientific realism? To answer, some history is relevant.

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Source: Achinstein P.. Evidence, Explanation, and Realism: Essays in Philosophy of Science. Oxford: Oxford University Press,2010. — 344 p.. 2010

IS THIS SCIENTIFIC REALISM?

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