Mark Siddall mes at zoo.toronto.edu
Thu May 18 22:32:13 EST 1995

In article <3pcssi$c4a at newstand.syr.edu> griffin at mailbox.syr.edu (David H. Griffin) writes:
>I think that Joe Felsenstein has touched on a frequently used and
>misused concept, "proof". In science, proof means test, as in test an
>hypothesis. This is related to the common usage of the word in

I am afraid I am going to have to dissent on this.  Prove does not
mean test.  "Prove" in  any framework means "prove true".
A notion that is quite clear from what Griffin writes below.

>When we do experiments to prove [test] an hypothesis the results may be
>contrary to the predictions of the hypothesis, and therefore disprove
>it. Alternatively, the results may be consistent with the predictions
>of the hypothesis and we accept the hypothesis as "true" until we can
>design a more discriminating test. In this sense the hypothesis has
>been proven [tested].

Not so.  
We do experiments to test a hypothesis.
If the results of the experiment are contrary to the hypothesis, then 
these results are taken as falsifiers of the hypothesis.  This does not
mean that the hypothesis is proven false.  Only that a falsifier has been
found.  Moreover, should the results of the experiment be consistent
with the hypothesis, the hypothesis simply has not been falsified.  It has not
been proven ("true" or otherwise).
Should a hypothesis be falsified, either the hypothesis is abandoned,
or the results are taken to be in error, or the hypothesis is then
modified to be compatible with the results.  This latter is the notion
of "ad hoc" expressed by Popper.  This is not to mean "willy nilly".
Regardless, at the end of the day, nothing is proven.  Nothing can be
taken as true.

Just so that this is not construed as a nihilistic viewpoint.  There
is a difference between "truth" and "understanding".

That is, testing, though it cannot lead to truth, can lead to understanding
and knowledge.

Proof and truth, however, are metaphysical, not scientific.
Test and falsification are scientific.
>Molecular phylogenetic analysis has proven repeatedly the truth of the
>prediction of evolutionary theory that closely related organisms have

A you see, "proven ... the truth".  Whereas I suggest that there is
no such truth to be had.

>greater similarity in genetic sequences than more distantly related
>organisms. Thus, when exceptions seem to occur in any particular

As a point of fact (which is not the same as truth either), that very
notion has been repeatedly falsified.  

>analysis, we have considerable confidence in booting the offenders out
>of the tree and placing them elsewhere, unless an alternative
>hypothesis can be formulated and tested. Occam's Razor often comes in

Ah... and there is the ad hoc.

>to play at this point.
>Lay audiences and scientists, too, often get confused over what is
>meant by proof.

As do others it would seem. :)

Mark E. Siddall                "I don't mind a parasite...
mes at vims.edu                    I object to a cut-rate one" 
Virginia Inst. Marine Sci.                     - Rick
Gloucester Point, VA, 23062

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