John F. Sowa wrote:
> Ravi,
>
> That's a good example:
>
> RS> For astronomers in India to work, two invisible planets called
> > RAHU and KETU were hypothesized and then only they could predict
> > eclipses or meridian crossings of stars.
>
> That is an example of the kind of unobservable entities that have
> been postulated for untold millennia. Another example is evil
> spirits or invisible microbes that cause disease. Examples from
> the early 20th century were electrons, protons, neutrons, positrons,
> and warped space-time. More recent examples include neutrinos and
> black holes. Postulated but undetected examples are strings,
> dark matter, dark energy, and multiple universes.
>
> Although evil spirits have not been detected and verified by
> subsequent studies, you could consider microbes to be a variant
> of the invisible spirits, benign and/or evil. You could even say
> that the toxins generated by the microbes are variants of evil
> potions, and the drugs used to control them are good potions
> that counter the evil.
>
> In the play Le Médecin malgré lui, Molière satirized the claim
> that opium puts people to sleep because it has "dormitive virtue."
>
> But Peirce made the point that postulating some yet unknown
> substance, such as dormitive virtue, is a useful first step.
> It focuses attention on the search for some component of opium
> that has that effect. That component was found and identified
> as morphine. The next step was to determine why morphine has
> the effects, and scientists later discovered that it chemically
> similar to internal chemicals, which they named "endorphins",
> which is short for "endogenous morphine".
>
> The practice of naming and postulating some as yet undetected
> substance or principle has been one of the most effective
> techniques of science for many centuries. The traditional
> medicines that were developed to counter "evil spirits" have
> often been shown to contain valuable chemicals that have been
> converted into modern drugs. And the centuries of experiments
> by the alchemists led to a long list of important chemicals and
> experimental techniques that are the foundation for chemsitry.
>
> The attempts by the positivists and logical positivists to
> eliminate unobservable entities and variables were decidedly
> wrong headed. But their ideas did have the useful effect of
> forcing scientists to demonstrate that the heuristic value
> of assuming and searching for as yet unobserved entities.
>
> In summary, the nominalist methodology of avoiding unobserved
> entities had a disastrous effect on psychology, but Einstein
> saved physics by his famous papers of 1905. In fact, Einstein
> criticized Bertrand Russell's "fear of metaphysics" (Angst vor
> der Metaphysik) as a disease (Krankheit).
>
> John
>
>
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