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of producing decisive theory-testing outcomes. Two manifestations of empirical underdetermination are conceptual vagueness and measurement error. All concepts have vagueness that can be reduced indefinitely but can never be eliminated completely. Mathematically expressed theories use measurement data that always contain measurement inaccuracy. Measurement error can be reduced indefinitely but never eliminated completely.

      Scientists prefer measurements and mathematically expressed theories, because they can measure the amount of prediction error in the theory, when the theory is tested. But separating measurement error from a theory’s prediction error can be problematic. Repeated careful execution of the measurement procedure, if the test is repeatable, enables statistical estimation of the degree or range of measurement error. A test is conclusive to the extent that the estimated measurement error is manifestly small relative to the produced effect in the test. But as in economics, repeated measurement is not always possible.

      4.20 Scientific Pluralism

      Scientific pluralism is recognition of the coexistence of empirically adequate alternative explanations due to undecidability permitted by the empirical undetermination in test-design language.

      All language is always empirically underdetermined by reality. Empirical underdetermination explains how two or more semantically alternative empirically adequate theories can have the same test-design language. This means that there are several theories yielding accurate predictions that are alternatives to one another, while having differences that are small enough to be within the range of the estimated measurement error. In such cases empirical underdetermination due to the current test design imposes undecidability on the choice among the alternative explanations.

      Econometricians are accustomed to alternative empirically adequate econometric models. This occurs because measurement errors in aggregate social statistics are large in comparison to those in natural sciences. Each such model has different equation specifications, i.e., different causal variables, and makes different forecasts for some of the same prediction variables that are accurate within the relatively large range of estimated measurement error. And discovery systems with empirical test procedures routinely proliferate empirically adequate alternative theories for output. They produce what Einstein called “an embarrassment of riches”. Logically this multiplicity of alternative theories means that there may be alternative empirically warranted nontruth-functional hypothetical conditional statements in the form “For all A if A, then C” having alternative antecedents “A” and making different but empirically adequate predictions that are the empirically indistinguishable consequents “C”.

      Empirical underdetermination is also manifested as conceptual vagueness. For example to develop his three laws of planetary motion Johannes Kepler, a heliocentrist, used the measurement observations of Mars that had been collected by Tycho Brahe, a type of geocentrist. Brahe had an awkward geocentric-heliocentric cosmology, in which the fixed earth is the center of the universe, the stars and the sun revolve around the earth, and the other planets revolve around the sun. But Kepler used Brahe’s astronomical measurement data, so measurement error was not the operative underdetermination permitting the alternative cosmologies. But Kepler was a convinced Copernican placing the sun at the center of the universe.

      Kepler’s belief in the Copernican heliocentric cosmology made the semantic parts contributed by that heliocentric cosmology become for him component parts of the semantics of the language used for celestial observation, thus displacing Brahe’s complicated combined geocentric-heliocentric cosmology’s semantical contribution. Then hypothesizing with the simpler Copernican heliocentrism’s clarifying contributions to the observational celestial semantics, he developed his three laws after deciding that the orbit is elliptical.

      Alternative empirically adequate theories due to empirical underdetermination are all more or less true. An answer as to which theory is truer must await further development of additional observational information or measurements that clarify the empirically inadequate test-design concepts. But there is never any ideal test design with “complete” information, i.e., with no vagueness or no measurement error. Pragmatist recognition of possible undecidability among alternative empirically adequate scientific explanations due to unavoidable empirical underdetermination is called the thesis of “scientific pluralism”.

      4.21 Scientific Truth

      Truth and falsehood are properties of statements, and admit to more or less.

      Tested and nonfalsified statements are more empirically adequate, have more realistic ontologies, and have more truth than falsified ones.

      Falsified statements have recognized error, and may simply be rejected unless they are still useful for their lesser realism and lesser truth.

      What is truth! Truth is a property of descriptive language with its relativized semantics and ontology. It is not merely a subjective expression of approval.

      Belief and truth are not identical. Belief is acceptance of a statement as true. But one may wrongly believe that a false statement is true, or wrongly believe that a true statement is false. Belief controls the semantics of the descriptive terms in universally quantified statements. Truth is the relation of a statement’s semantics to nonlinguistic reality. Furthermore as Jarrett Leplin maintains in his Defense of Scientific Realism, truth and falsehood are properties of statements that admit to more or less; they are not simply dichotomous, as they are represented in two-valued formal logic.

      Test-design language is presumed true with definitional force for the semantics of the test-design language, in order to identify the subject of the test. Theory language in an empirical test may be believed true by the developer and advocates of the theory, but the theory is not true simply by virtue of their belief. Belief in an untested theory is speculation about a future test outcome. A nonfalsifying test outcome will warrant belief that the tested theory is as true as the theory’s demonstrated empirical adequacy. Empirically falsified theories have recognized error, and may be rejected unless they are still useful for their lesser realism and lesser truth. Tested and nonfalsified statements are more empirically adequate, have ontologies that are more realistic, and thus are truer than empirically falsified statements.

      Popper said that Eddington’s historic eclipse test of Einstein’s theory of gravitation in 1919 “falsified” Newton’s theory and thus “corroborated” Einstein’s theory. Yet the U.S. National Aeronautics and Space Administration (NASA) today uses Newton’s laws to navigate interplanetary rocket flights such as the Voyager missions. Thus Newton’s “falsified” theory is not completely false or it could never have been used before or after Einstein. Popper said that science does not attain truth. But contemporary pragmatists believe that such an absolutist idea of truth is misconceived. Advancement in empirical adequacy is advancement in realism and in truth. Feyerabend said, “Anything goes”. Regarding ontology Hickey says, “Everything goes”, because while not all discourses are equally valid, there is no semantics utterly devoid of ontological significance. Therefore he adds that the more empirically adequate tested theory goes farther – is truer and more realistic – than its less empirically adequate falsified alternatives. As science grows in empirical adequacy, it thereby progresses in truth and in realism.

      4.22 Nonempirical Criteria

      Given the fact of scientific pluralism – of having several alternative explanations that are tested and not falsified due to empirical underdetermination in the test-design language – philosophers have proposed various nonempirical criteria they believe have been operative historically in explanation choice. And a plurality of untested and therefore unfalsified theories may also exist before any testing, so that scientists may have preferences for testing one theory over another based on nonempirical criteria. But no nonempirical criterion enables a scientist to predict reliably which alternative nonfalsified explanation will survive empirical testing, when in due course the degree of empirical underdetermination is reduced by a new or improved test design that enables decidable testing. To make such an anticipatory choice is like betting on a horse before it runs the race.

      Test designs are improved by developing

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