Who is the postivist?

Tom DiBenedetto tdib at UMICH.EDU
Mon Dec 8 16:04:40 CST 1997

 Richard Zander wrote:

> Parsimony eliminates grossly unreasonable
>trees, maximum likelihood eliminates grossly improbable trees.

I disagree with this. Parsimony selects the tree which represents the
set of least falsified grouping hypotheses.

>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.

"No convergence" is not an ad hoc hypothesis. An ad hoc hypothesis is
one which addresses a particular case and seeks to explain why it is
incompatable with a more general hypothesis. The general hypothesis
is homology. "No convergence" is a confirming explanation; it admits
that the evidence is explainable by the general hypothesis.

>Realists think there is a truth towards which the best hypothesis
>converges, anti-realists think truth is limited to the phenomena (data

Realists think there is a truth which we are trying to describe. It
is not necessary to assert that the best hypothesis is actually
converging on the truth, although we obviously try to develop our
science in such a way such that it does.
Anti-realists (by your definition) seem to deny the reality of taxa.
Once again, if that is your position, then why bother with

> 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.

But that is totally dependant on your calculation of probability. How
do you calculate that? Do you believe that life has had a single
history? Given that there are 30-80 million species, and more
possible phylogenies than quarks in the universe, how can any
phylogeny have a probability more than a smidgen above zero? And yet
one is true.

More information about the Taxacom mailing list