Circularity & testing.

Tom DiBenedetto tdib at UMICH.EDU
Sun Oct 20 21:37:19 CDT 1996

On Sun, 20 Oct 1996 16:17:24 -0700 (PDT), James Lyons-Weiler wrote:
>I think I understand the approach far better than you do.  Its circularity
>is clear to me, and I have yet to hear a reasoned argument to the
>contrary.  Proponents of metholodologies bear the responsibility of
>communicating the limitations of those methods these days, because it is
>commonly known that all methods of inference have limitations.  Why
>someone would ever act like a method does not have a limitation so
>blatantly obvious as circular reasoning escapes me.

Perhaps because it is the understanding of the method which is
escaping you? I'd like to help you out James, but I cant discuss
something which does not exist. You are the one making the charge, I
still dont see any point to your charge, so I have to simply await a
better argument.

>> >Homoplasies can be entirely homologous.
>> ??? I am at a total loss to understand this assertion. First of all
>> you discussed a set of "dead on" homologies. A cladogram of such a
>> set would exhibit no homoplasy, by definition. Furthermore, if all
>> the homologies were true, the tree would have to be true, contra your
>> original assertion. Now we have homoplasies? On that tree? and they
>> are entirely homologous? What do you mean?
>Your plastic definition of homology can't save the inference from being
>circular.  Completely convergent states can neverthess be homologous.
>Homoplasy in state can cause the cladogram to be wrong.

So what is plastic about my defintion? And how is my defintion
different from anyone elses? How can convergent states be homologus
when the two concepts are explicitly defined as opposites? And how
can "homoplasy in state" cause the cladogram to be wrong when
homoplasy is only identified on a cladogram? This is getting
bizarrerr and bizarrerrr....

Tom DiBenedetto
Fish Division
Museum of Zoology
University of Michigan

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