Achinstein's definition of scientific realism:

a doctrine committed at least to the claim that unobservable entities exist.

Three alternative definitions:
(1) Scientific realism is a view about truth and reference in scientific theories generally.
(Psillos, Laudan, Boyd). They are committed to at least the following claims:

(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 prede- cessors were successful insofar as they were successful.

Boyd adds:
(E) The reality which scientific theories describe is largely independent of our thoughts or theoretical commitments (op. cit., p. 42).

(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

(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 and Arthur Fine 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.


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Antirealists object to the following type of argument, for reasons addressed in the paper:

Eliminative-causal argument:

(1) Given what is known, the possible causes of effect E (for example, Brownian motion) are C, Cl,...C,, (for example, the motion of molecules, external vibrations, heat convection currents). (In probabilistic terms, given what is known, the probability is high that E is caused by one of the Cs cited.)
(2) C1l...,Cn do not cause E (since E continues when these factors are absent or altered). So probably
(3) C causes E.

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Reply. An antirealist who argues in the previous manner looks at the situation as one involving so-called stratified sampling. The population of As is divided into two classes or strata: the observables and the unobservables (if any). To make inferences about the entire class of As with respect to a property B, the antirealist is claiming, one needs to select randomly members from both strata for observation. Since one cannot select unobservable members for observation, one cannot legitimately, without potential bias, make inferences about this stra- tum, but only about the observable stratum. (14)

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The scientific realism implicit in Perrin's arguments can be put like this:
(1) There are unobservables (for example, molecules).
(2) Their existence and their properties can be inferred (only) on empirical grounds, in some cases from experiments, so that a claim to know they exist and have these properties is justified.
(3) A legitimate mode of reasoning that can be used for this purpose involves two important components:

• (a) causal-eliminative reasoning to the existence of the postulated entity, and to certain claims about its properties, from other experimental results;
• (b) an argument to the conclusion that the particular experimental results obtained are very probable given the existence of the postulated entity and properties.