Twentieth-Century Philosophy of Science: A History (Third Edition). Thomas J. Hickey

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      4.17 Semantics of Empirical Testing

      Much has already been said about the artifactual character of semantics, about componential semantics, and about semantical rules. In the semantical discussion that follows these concepts are brought to bear upon the discussion of empirical testing and test outcomes.

      If a test has a nonfalsifying outcome, then the semantics of the tested theory is unchanged for the theory’s developer and advocates. Since they had proposed the theory in the belief that it would not be falsified, their belief in the theory makes it function for them as a set of semantical rules. Thus for them both the theory and the test design are accepted as true, and after the nonfalsifying test outcome both sets of statements continue to contribute parts to the complex meanings of the descriptive terms common to both theory and test design, as before the test.

      But when the test outcome is a falsification, there is a semantical change produced in the theory for the developer and advocates of the tested theory who accept the test outcome as a falsification. The unchallenged test-design statements continue to contribute semantics to the terms common to the theory and test design by contributing their parts to the meaning complexes of each of the common terms. But the component parts of those meanings contributed by the falsified theory statements are excluded from the semantics of those common terms for the proponents who no longer believe in the theory due to the falsifying test outcome.

      4.18 Test Design Revision

      Empirical tests are conclusive decision procedures only for scientists who agree on which language is proposed theory and which language is presumed test design, and who furthermore accept both the test design and the test-execution outcomes produced with the accepted test design.

      The decidability of empirical testing is not absolute. Popper had recognized that the statements reporting the observed test outcome, which he called “basic statements”, require prior agreement by the cognizant scientists, and that those basic statements are subject to future reconsideration.

      Theory language is relatively more hypothetical than test-design language, because the interested scientists agree that in the event of a falsifying test outcome, revision of the theory will likely be more productive than revision of the test-design language.

      For the scientist who does not accept a falsifying test outcome of a theory, a different semantical change is produced than if he had accepted the test outcome as a falsification. Such a dissenting scientist has either rejected the report of the observed test outcome or reconsidered the test design. If he rejects the outcome of the individual test execution, he has merely questioned whether or not the test was executed in compliance with its agreed test design. Repetition of the test with greater fidelity to the design may answer such a challenge to the test’s validity one way or the other.

      But if in response to a falsifying test outcome the dissenting scientist has reconsidered the test design itself, then he has thereby changed the semantics involved in the test in a fundamental way. Reconsideration of the test design amounts to rejecting the test design as if it were falsified, and letting the theory define the subject of the test and the problem under investigation – a rôle reversal in the pragmatics of test-design language and theory language. Then the theory’s semantics characterizes the problem for the dissenter, and the test design is effectively falsified, because it is deemed inadequate thus making the test design and the test execution irrelevant.

      If a scientist rejects a test design in response to a falsifying test outcome, he has made the theory’s semantics define the subject of the test and the problem under investigation.

      Popper rejects such a dissenting response to a test, calling it a “content-decreasing stratagem”. He admonishes that the fundamental maxim of every critical discussion is that one should “stick to the problem”. But as James Conant recognized to his dismay in his On Understanding Science: An Historical Approach the history of science is replete with such prejudicial responses to scientific evidence that have nevertheless been productive and strategic to the advancement of basic science in historically important episodes. The prejudicially dissenting scientists may decide that the design for the falsifying test supplied an inadequate description of the problem that the tested theory is intended to solve, often if he developed the theory himself and did not develop the test design. The semantical change produced for such a recalcitrant believer in the theory affects the meanings of the terms common to the theory and test-design statements. The parts of the meaning complex contributed by the test-design statements are then the parts excluded from the semantics of one or several of the descriptive terms common to the theory and test-design statements. Such a semantical outcome for a tested theory can indeed be said to be “content-decreasing”, as Popper said.

      But a scientist’s prejudiced or tenacious rejection of an apparently falsifying test outcome may have a contributing function in the development of science. It may function as what Feyerabend called a “detecting device”, a practice he called “counterinduction”, which is a discovery strategy that he illustrated in his examination of Galileo’s arguments for the Copernican cosmology. Galileo used the apparently falsified heliocentric theory as a “detecting device” by letting his prejudicial belief in the heliocentric theory control the semantics of observational description. This enabled Galileo to reinterpret observations previously described with the equally prejudiced alternative semantics built into the Aristotelian geocentric cosmology. Counterinduction was also the strategy used by Heisenberg, when he reinterpreted the observational description of the electron track in the Wilson cloud chamber using Einstein’s thesis that the theory decides what the physicist can observe, and he then developed his indeterminacy relations using quantum concepts.

      Another historic example of using an apparently falsified theory as a detecting device is the discovery of the planet Neptune. In 1821, when Uranus happened to pass Neptune in its orbit – an alignment that had not occurred since 1649 and was not to occur again until 1993 – Alexis Bouvard developed calculations predicting future positions of the planet Uranus using Newton’s celestial mechanics. But observations of Uranus showed significant deviations from the predicted positions.

      A first possible response would have been to dismiss the deviations as measurement errors and preserve belief in Newton’s celestial mechanics. But astronomical measurements are repeatable, and the deviations were large enough that they were not dismissed as observational errors. They were recognized to be a new problem.

      A second possible response would have been to give Newton’s celestial mechanics the hypothetical status of a theory, to view Newton’s law of gravitation as falsified by the anomalous observations of Uranus, and then attempt to revise Newtonian celestial mechanics. But by then confidence in Newtonian celestial mechanics was very high, and no alternative to Newton’s physics had been proposed. Therefore there was great reluctance to reject Newtonian physics.

      A third possible response, which was historically taken, was to preserve belief in the Newtonian celestial mechanics, propose a new auxiliary hypothesis of a gravitationally disturbing phenomenon, and then reinterpret the observations by supplementing the description of the deviations using the auxiliary hypothesis of the disturbing phenomenon. Disturbing phenomena can “contaminate” even supposedly controlled laboratory experiments. The auxiliary hypothesis changed the semantics of the test-design description with respect to what was observed. In 1845 both John Couch Adams in England and Urbain Le Verrier in France independently using apparently falsified Newtonian physics as a detecting device made calculations of the positions of a disturbing postulated planet to guide future observations in order to detect the postulated disturbing body. In September 1846 using Le Verrier’s calculations Johann Galle observed the postulated planet with the telescope at the Berlin Observatory.

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