Who is the postivist?

Richard Zander bryo at COMMTECH.NET
Mon Dec 8 08:06:33 CST 1997

Tom DiBenedetto wrote:

> >From my understanding, positivists can be usefully distinguished from
> Popperian critical rationalists by the former's adherence to a
> verificationist approach to assesing the validity of scientific
> theories, as opposed to Popperian falisificationism. In modern
> phylogenetics, it is (some) cladists who stress the falsificatinist
> approach, whereas the statistical phylogeneticists (those lost in the
> Felsenstein zone) seem to be inherently verificationist.

I think they are both wrong. Parsimony eliminates grossly unreasonable
trees, maximum likelihood eliminates grossly improbable trees. The pool
of trees 1 step (or 2 steps) longer than the shortest tree and the pool
of "credible trees" (with posterior probability adding to 95%, are
similar. No one ever assumes that, say, a radiocarbon date with sigma
values (e.g.
6970+or-760), converges on the truth with the central value
approximating the truth. The truth is, probably, somewhere in the range
(probability density) indicated. Likewise, statistical phylogeneticists
select one tree, the tree of maximum likelihood, in my opinion, solely
because cladists are seemingly able to select one tree, and you are both
competing for grants.
Ideally, statistical phylogeneticists can demonstrate as a probabilistic
hypotheses only where all the trees in at least the 50% credible zone
agree (and 95% if they actually want "results" as a theory, not just a
hypotheses). And cladists...I don't see a way to select one tree as a
reconstruction. Every elimination from the set of reasonable trees is an
ad hoc assumption of no convergence.

> With James's interest in the "truth", in terms of the "windows to the
> past", I would suggest investigating Popper's notion of
> "verisimilitude"; which is basically the substitute for "truth",
> since truth is unknowable. Verisimilitude is a notion of "closeness
> to truth" and Popper develops a logical calculus for it. I havent had
> time to develop arguments around this concept, but I suspect it will
> be useful for justifying cladistic parsimony approches.

Realists think there is a truth towards which the best hypothesis
converges, anti-realists think truth is limited to the phenomena (data
set). Quine, our chief pragmatist,  says he is a realist and there are
realities "out there", however, truth is corrigible, meaning you believe
because of facts but a scientist should be willing to change his/her
mind about reality with new information. What does all this mean? Sure
sounds like weaseling to me, and Quine is an antirealist who says he
isn't. I figure comments on truth are much alike, and help little. What
is important is that Realists have lower standards for hypotheses than
Antirealists. As long as you can demonstrate an increase in probability
(lower falsifiability, whatever), you can select the best example as
best explanation and therefore asseverate one tree as "approximately the
truth." Even when the one tree has a low probability of being the truth.
This is scientifically unconscionable.


Richard H. Zander, Buffalo Museum of Science
1020 Humboldt Pkwy, Buffalo, NY 14211 USA bryo at commtech.net

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