More on realism

Tom DiBenedetto tdib at UMICH.EDU
Thu Dec 11 05:21:31 CST 1997

Richard Zander wrote:

>A realist believes in a reality based on all the facts at
>one's disposal, then changes the concept when more facts appear and make
>it necessary.

No that is not my understanding of realism. I consider myself a
realist. I do not believe that reality is based on facts. A fact is
simply an idea which is deemed to be so well corroborated that it is
accepted without further investigation (unless new phenomena
impress upon us a reason to reopen the issue).
Rather, I believe facts are based on reality, or our perceptions, and
tested hypotheses concerning the reality that is accessable to us.

>> What exactly are you denying the reality of?

>... We can agree on what works,
>pragmatically, and on what can be used (instrumentalism) be it ideas or
>material things, to effect changes in our lives. We jointly aim at a classification of >organisms that facilitates prediction.

Prediction of what? A parsimonious ordering of homologies has, it
seems to me, the greatest predictive power of any ordering system.

>To the extent, however, that philosophical
>realists among cladists claim to have approached truth more closely than
>I think they have approached truth (with a view to furthering a joint
>effort), I complain.

As a cladist, I find my hypotheses to be believable to the extent
that they are tested, and corroborated. I cant imagine a
quantification of the distance I am from the truth, but I feel it is
justified to prefer hypotheses which survive critical testing better
than others; i.e. the most parsimonious tree.

>All sentences are theory-laden. I call for an INDEPENDENT TEST OF
>predictability of the trees obtained is compared and evaluated in such a
>way that we can feel the work is worthwhile.

Could you flesh this out a bit? Sounds to me like you are simply
asking for more characters (for that is what they are).

>I predict that fine structure of trees from
>both maximum parsimony and maximum likelihood analysis will not be worth
>much as far as prediction goes.

I think that is clearly nonsense. They already have (at least the
parsimony trees).

>> is adjudged to have low probability in light of some theory,,why does
>> this indicate that it is false? Maybe the theory underlying the
>> probability calculation is false.

>>Maybe so. In fact, I'm surprized that both cladists and statistical
>phylogeneticists don't shuffle their feet and look ashamed more often.

This doesnt follow. Cladists dont calculate probabilities,
understanding as we do, how illegitimate a frequency probability for
unique historical data is.

>>You seem to beleive that you can calculate the probability of
>> something being TRUE. How can an anti-realist hold such a position?

>Good retort. Answer is I think I can calculate the PROBABILITY of
>something being true. Note emphasis.

The emphasis wont save you. It will still be the probability of
something being true under the assumptions of some theory.

> However, a big however, calculating
>probabilities of things that happened ONCE in the PAST could be

IS laughable...

>without the potential of molecular data from say a couple of
>independent, selectively neutral genes.

And just what on earth do you imagine that a couple of neutral genes
tell you? The probability that a given tree would represent the
average phylogeny if we could run through the history of life a
thousand times?

Tom DiBenedetto       
Fish Division                                   tdib at
University of Michigan Museum of Zoology

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